My MacBook is stuck on grey screen with rotating circle

My MacBook is stuck on grey screen with rotating circle

See this Apple note on dealing with that.  If you have OS X 10.8 Mountain Lion, this is the equivalent note, howver, it's not as detailed.

Similar Messages

  • Downloaded OSX Mountain Lion on MacBook now stuck on grey screen with spinning wheel HELP?!?!

    Downloaded OSX Mountain Lion on MacBook now stuck on grey screen with spinning wheel. What can I do, will I loose everything on my laptop?

    ashg23 wrote:
    Thank you, I have restarted but it is still stuck at the grey page with the spinning wheel? Any idea?
    Have you started up holding down Command + R and attempted to install again?
    Pete

  • Macbook Pro stuck on grey screen with Apple logo

    Macbook Pro was purchased in mid-late 2009 and is running on OS X 10.6. Today is suddenly stopped responding and so I turned it off. When I turned it back on it opend to the grey screen with the Apple logo and the loading icon and that is where it stayed. I have been searching for the answer on different forums but have yet to find a solution. My hard drive is appearing in the Disk Utility but not in the box when I try to reinstall OS X. Any suggestions on what to do?

    Create a data recovery, undelete boot drive
    dustysjuls wrote:
    Will that erase all of the files on my hard drive? Or will it just erase and reinstall the operating system? I do not have my files backed up.
    A #18 Reinstall Just OS X, details here:
    Step by Step to fix your Mac

  • My macbook pro is stuck on grey screen with apple symbol in center with the progress circle under it continusly spinning. After I had turned it on. Prior to turning it on I had to force close and shut down a few hours prior. Please Help?

    My macbook pro is stuck on grey screen with apple symbol in center with the progress circle under it continusly spinning. After I had turned it on. Prior to turning it on I had to force close and shut down a few hours prior. Please Help I have tried everything I know to do

    Unfortunately this means that there is a problem in the boot sector of your hard drive. It might be indicative of a fundamental corruption in the coding that allows your computer to boot your operating system from your hard drive. I had this problem twice and it resulted in me having to get a new hard drive and restore my data.
    In other words, your computer can't talk to your operating system so you can't access your data.
    Here is my advice: DON'T CALL APPLE TECH SUPPORT though they are kind and usually helpful it will take you an hour just to explain the situation and they will only tell you to do what I'm gonna say here.
    First: Shut down your computer completely
    Two: boot up while holding down the following keys: command, option, p, and r. The computer will reboot 3 times. This solution will likely fail so if you're frustrated skip to the next step.
    Three: Boot up while holding down the option key. Select recovery drive. Select your default language. Select disk utility, click on Macintosh HD, and select "verify and repair volume." Likely the verification will produce some line like "unused node not erased." Or something like that. If anything using the words "node structure" comes up, you need a new hard drive.
    If after verification and repairs you still can't boot I sincerely hope you have apple care because you will need a new hard drive. Set up an appointment to come in to the apple store, they will tell you to go and get data recovery, just ask them to give you the old hard drive. Unless you have an up to date backup in which case you can just restore from that. If you're lucky the only issue is with the boot sector which means that if you ask them to give you the old hard drive, you can buy an enclosure and you have effectively been given a free external hard drive. It still works to store data just not to load an operating system.
    If you have a back up drive bring it to the apple store and they'll do the whole thing right there, it should take around an hour and a half but may take longer.
    Hope this helps, it's annoying but it's your safest bet.
    All the best.

  • I have snow leopard installed as an OS.  When trying to reboot a MacBook Pro I am getting stuck on grey screen with apple logo and rotating symbol.  What can I do?

    I have snow leopard installed as an OS.  When trying to reboot a MacBook Pro I am getting stuck on grey screen with apple logo and rotating symbol.  What can I do?

    Maybe this might help.
    http://support.apple.com/kb/TS2570

  • MacBook Pro has a grey screen with circle and slash and will not start up or start into safe mode.

    MacBook Pro has started to get a grey screen with circle and slash and will not start up or start into safe mode.  This happened once previously, however, it allowed a safe mode reboot and then worked for a week or so.  While utilzing the machine, it started with the spinning beach ball for about 5 minutes, went into a shut down mode and then rebooted and came back up with the grey screen with a circle and slash after a few minutes.  For the past three days it has been stuck and will not allow it to boot into safe mode.  Any idea or suggestions?

    Try starting the MBP with the OPTION key down.  If you see two HDD icons, select the recovery Icon.  From the 4 option menu, select Disk Utility.  Select Disk Utility>First Aid and run Verify and Repair. 
    If you cannot get into the recovery partition, make an appointment at an Apple store genius bar.
    Ciao.

  • G5 start up problem: stuck at grey screen with fans running full strength

    hi, i'm new to discussions, so i hope this question and my technical knowledge and descriptions will be OK: problem: G5 20" stuck at grey screen with fans running full strength..
    so far i've tried but did not work:
    - power off by pressing the button for 5 secs,
    - checked all cables connections etc, take out the power cable try again, etc.
    - removed all USB connections, re-did
    - tried to use it as 'target drive' connected to my macbook by firewire
    - tried to start up and keeping C key pressed
    - tried to start up with 'shift' key pressed
    - tried to start up with command, options, P and R keys pressed,
    - i had an additional RAM, i've taken it out and tried again, no luck
    - i've put in Mac OS X install disc1, no luck, and now disc is inside my iMac, can't take it out
    any recommendations? thank you!

    Scroto,
    You may not actually have a bad processor. On the Dual G5's it's not uncommon after a few years for dust and corrosion to build up between the processors and their sockets. You can fairly easily remove the processors and clean the connections yourself if you're at all handy. Basically, snap off the heatsink covers, loosen a few screws and the processor and heatsink come out as a unit.
    Clean the contacts on the processors (carefully). And clean the sockets. Be sure to put the same processor in the same place or you'll have issues.
    I used 90% isopropol alcohol to clean mine last year. Let it air dry and blew both the socket and the cpu off after with canned air. That done, I reinstalled the processors, buckled everything up and no more "bad" processor... The machine worked perfectly from then on and I assume it still does today. Don't know, someone stole it last month:(...

  • Start up screen stuck on grey screen with apple logo and spinning gear

    Start up screen is stuck on grey screen with apple logo and spinning gear. What should I do?

    See this thread with dominic23’s suggestions:  https://discussions.apple.com/thread/5783326?tstart=0

  • Intel-based iMac stuck in grey screen with spinning wheel. SMC::smcReadKeyAction ERROR THOP kSMBadArgumentError(0x89)

    Hi guys,
    since yesterday my Intel-Based iMac doesn't boot normally, its stuck in grey screen with a spinning wheel.
    Its an Intel-based iMac 21.5'' purchased in 2011, and i recently (2 months ago) upgraded it to Mavericks.
    -2 weeks ago, i installed smcFanControl app
    -Tried start up in Safe Mode by holding Shift but its not working. i think i hear fans are working more than they were before the problem occurs.
    -entered Single User Mode and i get an error
    SMC ::smcReadKeyAction ERROR THOP kSMCBadArgumentError(0x89) fKeyHashTable=0x0xffffff8029fa1000
    -followed some instructions found online, but can execute the correct commands in SingleUserMode
    tried to remove FanControl as explained here: http://apple.stackexchange.com/questions/110667/errorr-kernel-smcsmcreadkeyactio n-in-console
    any ideas what may caused this and how can i fix this?
    Thanks in advance

    Take each of these steps that you haven't already tried. Stop when the problem is resolved.
    Step 1
    The first step in dealing with a startup failure is to secure the data. If you want to preserve the contents of the startup drive, and you don't already have at least one current backup, you must try to back up now, before you do anything else. It may or may not be possible. If you don't care about the data that has changed since the last backup, you can skip this step.   
    There are several ways to back up a Mac that is unable to start. You need an external hard drive to hold the backup data.
         a. Start up from the Recovery partition, or from a local Time Machine backup volume (option key at startup.) When the OS X Utilities screen appears, launch Disk Utility and follow the instructions in this support article, under “Instructions for backing up to an external hard disk via Disk Utility.” The article refers to starting up from a DVD, but the procedure in Recovery mode is the same. You don't need a DVD if you're running OS X 10.7 or later.
    b. If Step 1a fails because of disk errors, and no other Mac is available, then you may be able to salvage some of your files by copying them in the Finder. If you already have an external drive with OS X installed, boot from it. Otherwise, if you have Internet access, follow the instructions on this page to prepare the external drive and install OS X on it. You'll use the Recovery installer, rather than downloading it from the App Store.
    c. If you have access to a working Mac, and both it and the non-working Mac have FireWire or Thunderbolt ports, start the non-working Mac in target disk mode. Use the working Mac to copy the data to another drive. This technique won't work with USB, Ethernet, Wi-Fi, or Bluetooth.
    d. If the internal drive of the non-working Mac is user-replaceable, remove it and mount it in an external enclosure or drive dock. Use another Mac to copy the data.
    Step 2
    If the startup process stops at a blank gray screen with no Apple logo or spinning "daisy wheel," then the startup volume may be full. If you had previously seen warnings of low disk space, this is almost certainly the case. You might be able to start up in safe mode even though you can't start up normally. Otherwise, start up from an external drive, or else use the technique in Step 1b, 1c, or 1d to mount the internal drive and delete some files. According to Apple documentation, you need at least 9 GB of available space on the startup volume (as shown in the Finder Info window) for normal operation.
    Step 3
    Sometimes a startup failure can be resolved by resetting the NVRAM.
    Step 4
    If you use a wireless keyboard, trackpad, or mouse, replace or recharge the batteries. The battery level shown in the Bluetooth menu item may not be accurate.
    Step 5
    If there's a built-in optical drive, a disc may be stuck in it. Follow these instructions to eject it.
    Step 6
    Press and hold the power button until the power shuts off. Disconnect all wired peripherals except those needed to start up, and remove all aftermarket expansion cards. Use a different keyboard and/or mouse, if those devices are wired. If you can start up now, one of the devices you disconnected, or a combination of them, is causing the problem. Finding out which one is a process of elimination.
    Step 7
    If you've started from an external storage device, make sure that the internal startup volume is selected in the Startup Disk pane of System Preferences.
    Start up in safe mode. Note: If FileVault is enabled, or if a firmware password is set, or if the startup volume is a Fusion Drive or a software RAID, you can’t do this. Post for further instructions.
    Safe mode is much slower to start and run than normal, and some things won’t work at all, including wireless networking on certain Macs.
    The login screen appears even if you usually log in automatically. You must know the login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.
    When you start up in safe mode, it's normal to see a dark gray progress bar on a light gray background. If the progress bar gets stuck for more than a few minutes, or if the system shuts down automatically while the progress bar is displayed, the startup volume is corrupt and the drive is probably malfunctioning. In that case, go to Step 10. If you ever have another problem with the drive, replace it immediately.
    If you can start and log in in safe mode, empty the Trash, and then open the Finder Info window on the startup volume ("Macintosh HD," unless you gave it a different name.) Check that you have at least 9 GB of available space, as shown in the window. If you don't, copy as many files as necessary to another volume (not another folder on the same volume) and delete the originals. Deletion isn't complete until you empty the Trash again. Do this until the available space is more than 9 GB. Then restart as usual (i.e., not in safe mode.)
    If the startup process hangs again, the problem is likely caused by a third-party system modification that you installed. Post for further instructions.
    Step 8
    Launch Disk Utility in Recovery mode (see Step 1.) Select the startup volume, then run Repair Disk. If any problems are found, repeat until clear. If Disk Utility reports that the volume can't be repaired, the drive has malfunctioned and should be replaced. You might choose to tolerate one such malfunction in the life of the drive. In that case, erase the volume and restore from a backup. If the same thing ever happens again, replace the drive immediately.
    This is one of the rare situations in which you should also run Repair Permissions, ignoring the false warnings it may produce. Look for the line "Permissions repair complete" at the end of the output. Then restart as usual.
    Step 9
    Reinstall the OS. If the Mac was upgraded from an older version of OS X, you’ll need the Apple ID and password you used to upgrade.
    Step 10
    Do as in Step 9, but this time erase the startup volume in Disk Utility before installing. The system should automatically restart into the Setup Assistant. Follow the prompts to transfer the data from a Time Machine or other backup.
    Step 11
    This step applies only to models that have a logic-board ("PRAM") battery: all Mac Pro's and some others (not current models.) Both desktop and portable Macs used to have such a battery. The logic-board battery, if there is one, is separate from the main battery of a portable. A dead logic-board battery can cause a startup failure. Typically the failure will be preceded by loss of the settings for the startup disk and system clock. See the user manual for replacement instructions. You may have to take the machine to a service provider to have the battery replaced.
    Step 12
    If you get this far, you're probably dealing with a hardware fault. Make a "Genius" appointment at an Apple Store, or go to another authorized service provider.

  • Imac 2008 stuck on grey screen with spinning wheel no discs I lost them

    HI, I have a imac 2008 24" someone help please.stuck on grey screen with spinning wheel after 5 minutes mac just restarts again.I have no restore dvds as I borrowed them out and never got them back thanks

    If you are in the US call Apple Customer Support 1-800-767-2775, provide the Serial Number and specifications of the Mac, and for a reasonable fee, they will supply a replacement set of system discs (if available).
    The discs will be for the original version of the OS that was pre-installed when the Mac was manufactured.
    If you are in another country:
    http://support.apple.com/kb/HE57
    Useful article here on the causes of the Spinning Beach Ball and how to troubleshoot it:
    http://www.computerworld.com/s/article/9177479/Troubleshoot_the_spinning_beach_b all?taxonomyId=89&pageNumber=1
    and also this:
    http://www.thexlab.com/faqs/sbbod.html

  • Gets stuck on grey screen with logo after restore.

    I restored my 2008 macbook and reinstalled OS X lion onto it. It downloaded items for lion and automatically restarted. When it restarted it got stuck on a grey screen with the apple logo and a spinning circle. I turned the computer off and attempted to restart again, same outcome. I restarted it again and pressed command option p r (saw it from other posts on here) and it brought me back to the screen where I can reinstall OS X lion, go to utilities, etc. So I clicked reimstall lion and it did its thing and automatically restarted. Then like last time it got stuck on the grey screen with the logo and spinning circle.ugh! What am I doing wrong? Please help.

    Restarted it again with the p r command option brought me to the installing screen again and then said "there was an error installing please try agian" please any help is aporeciated, I have my files on an external hard drive but I need to be able to access my computer so I can continue applying to jobs/access my resume on the external hard drive and it is my only way to talk to my deployed husband besides email on my phone.
    I also clicked repair disk in utilities and it says "the volume Mac os x base system appears to be OK" It will not bring me to the thing where I have the option to reinstall lion. I restarted and its yet again stuck on the grey screen with apple logo and spinning circle.

  • Stuck on grey screen with apple logo when starting up?

    Hi,
    My Macbook (2009 aluminium unibody (Leopard 10.5.8)) won't boot. When I try to start it up it gives the chime and then gets stuck at the grey screen with the Apple logo and some spinning gear below. I have tried booting with the install DVD and repairing through Disk Utility but this doesn't work. Disk Utility can see the hard drive but none of the partitions on it! This makes me think the hard drive has died.
    However, I can still boot to Windows through BootCamp. From Windows 7 I can still see and access files from the Mac partition. So maybe the hard drive is ok and something else needs fixing... SATA cable???
    Other info:
    The night before this happened my computer froze when trying to shut down from Windows and I had to force shut down.
    The current internal hard drive is only about 4 months old (a bit short for it to be dying already - its a Western Digital 750gb 7200rpm). I replaced the old one as it had stopped working (at least i thought it was the hard drive ). The hard drive I replaced had lasted about 2 years (Seagate 500gb 7200rpm). Maybe the 7200rpm gets too hot?
    Any help much appreciated as I really don't want to be reinstalling again.
    Thanks

    Boot from the OS dvd and start the install process, but stop immediately after the language selection. (You are not reinstalling.) At this point you will see a Utilities menu. Open Disk Utility, select your start up disk, and click on Repair Disk. When that is done, quit DU and restart.
    See if that procedure will let you boot as usual.

  • MacBook Air stuck in grey screen after ML installation

    Hi everybody,
    I have downloaded and installed Mountain Lion on my MacBook Air (2011). After the installation the computer restarted and stuck in the grey loading screen, showing the apple logo and the turning wheel. I've left it alone for hours but nothing happens. This is still the case and I cannot find a way out.
    Here is what I have tried so far:
    - Reload and reinstall ML via recovery mode (twice). Recovery mode shows me that 10.8 is installed, by the way
    - Restart without peripherals connected
    - Reset PRAM and NVRAM
    - Disconnect all cables and let the computer rest
    - Diagnose and repair hard drive (showed me a message that a Java-related group has a value of 80 but should be 0. Repair was "successful")
    - Safe boot (A bar appears in loading screen but disappears after it is about halfway full and I'm back in grey screen)
    Unfortunately none of this worked. I have a Time Machine backup but it is located at the other end of the country (long story) and I can't access it easily.
    Do you guys have any more ideas what else I could try? I'd really appreciate it.
    Thanks!
    B4sti

    I'm having the same issue. My MacBook air is stuck on the grey screen with the apple logo. I've waited for hours. Has anyone found a resolution to this issue?

  • My macbook pro 2011 shows grey screen with apple logo and want start

    i was just using my macbook pro and it freezed for a while not responding and i turned it off by pressing the power button. afterwards, i turn it on and it shows a grey screen with apple logo but want start pls somebody help me because am having "my life" on the machine

    Take each of these steps that you haven't already tried. Stop when the problem is resolved.
    Step 1
    The first step in dealing with a boot failure is to secure your data. If you want to preserve the contents of the startup drive, and you don't already have at least one current backup, you must try to back up now, before you do anything else. It may or may not be possible. If you don't care about the data that has changed since your last backup, you can skip this step.   
    There are several ways to back up a Mac that is unable to boot. You need an external hard drive to hold the backup data.a. Boot into Recovery by holding down the key combination command-R at the startup chime, or from a local Time Machine backup volume (option key at startup.) Release the keys when you see a gray screen with a spinning dial. When the OS X Utilities screen appears, launch Disk Utility and follow the instructions in this support article, under “Instructions for backing up to an external hard disk via Disk Utility.”
    b. If you have access to a working Mac, and both it and the non-working Mac have FireWire or Thunderbolt ports, boot the non-working Mac in target disk mode by holding down the key combination command-T at the startup chime. Connect the two Macs with a FireWire or Thunderbolt cable. The internal drive of the machine running in target mode will mount as an external drive on the other machine. Copy the data to another drive. This technique won't work with USB, Ethernet, Wi-Fi, or Bluetooth.
    c. If the internal drive of the non-working Mac is user-replaceable, remove it and mount it in an external enclosure or drive dock. Use another Mac to copy the data.
    Step 2
    Press and hold the power button until the power shuts off. Disconnect all wired peripherals except those needed to boot, and remove all aftermarket expansion cards. Use a different keyboard and/or mouse, if those devices are wired. If you can boot now, one of the devices you disconnected, or a combination of them, is causing the problem. Finding out which one is a process of elimination.
    If you've booted from an external storage device, make sure that your internal boot volume is selected in the Startup Disk pane of System Preferences.
    Step 3
    Boot in safe mode.* The instructions provided by Apple are as follows:
    Shut down your computer, wait 30 seconds, and then hold down the shift key while pressing the power button.
    When you see the gray Apple logo, release the shift key.
    If you are prompted to log in, type your password, and then hold down the shift key again as you click Log in.
    Safe mode is much slower to boot and run than normal, and some things won’t work at all, including wireless networking on certain Macs.
    The login screen appears even if you usually log in automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.
    *Note: If FileVault is enabled, or if a firmware password is set, or if the boot volume is a software RAID, you can’t boot in safe mode. Post for further instructions.
    When you boot in safe mode, it's normal to see a dark gray progress bar on a light gray background. If the progress bar gets stuck for more than a few minutes, or if the system shuts down automatically while the progress bar is displayed, your boot volume is damaged and the drive is probably malfunctioning. In that case, go to step 5.
    If you can boot and log in now, empty the Trash, and then open the Finder Info window on your boot volume ("Macintosh HD," unless you gave it a different name.) Check that you have at least 9 GB of available space, as shown in the window. If you don't, copy as many files as necessary to another volume (not another folder on the same volume) and delete the originals. Deletion isn't complete until you empty the Trash again. Do this until the available space is more than 9 GB. Then reboot as usual (i.e., not in safe mode.)
    If the boot process hangs again, the problem is likely caused by a third-party system modification that you installed. Post for further instructions.
    Step 4
    Sometimes a boot failure can be resolved by resetting the NVRAM.
    Step 5
    Launch Disk Utility in Recovery mode (see step 1.) Select your startup volume, then run Repair Disk. If any problems are found, repeat until clear. If Disk Utility reports that the volume can't be repaired, the drive has malfunctioned and should be replaced. You might choose to tolerate one such malfunction in the life of the drive. In that case, erase the volume and restore from a backup. If the same thing ever happens again, replace the drive immediately.
    This is one of the rare situations in which you should also run Repair Permissions, ignoring the false warnings it may produce. Look for the line "Permissions repair complete" at the end of the output. Then reboot as usual.
    Step 6
    Boot into Recovery again. When the OS X Utilities screen appears, follow the prompts to reinstall the OS. If your Mac was upgraded from an older version of OS X, you’ll need the Apple ID and password you used to upgrade.
    Note: You need an always-on Ethernet or Wi-Fi connection to the Internet to use Recovery. It won’t work with USB or PPPoE modems, or with proxy servers, or with networks that require a certificate for authentication.
    Step 7
    Repeat step 6, but this time erase the boot volume in Disk Utility before installing. The system should automatically reboot into the Setup Assistant. Follow the prompts to transfer your data from a backup.
    Step 8
    A dead logic-board battery in a Mac Pro can cause a gray screen at boot. Typically the boot failure will be preceded by loss of the startup disk and system clock settings. See the user manual for replacement instructions.
    Step 9
    If you get this far, you're probably dealing with a hardware fault. Make a "Genius" appointment at an Apple Store to have the machine tested.

  • MBP (2010) stuck in grey screen with Apple logo no matter what I do.

    Hi everybody,
    I know this issue has been posted many times in the past, and I have searched everywhere, but I am quickly running out of option but to repartition/reformat and do a clean install. I have important files on my computer (I know! Back up! Back up! Back up!) and need your help to preferably regain full access to my system or somehow find access to my files so I could transfer them to an external hdd.
    From two days ago my as I was browing the net through Google Chrome my computer all of a sudden started to show the sippinig beach ball and became completely unresponsive. I could not force shut down any program or restart the system. So, I held down the power button and forced the system to shut down. When I rebooted the MB it all began going haywire. The boot process gets stuck in a grey screen with the Apple logo and the spinning wheel (not the beach ball) for a long time. After that I get the mouse pointer, and if I move that it turns to the spinning beach ball and nothing happens except that the screen flashes between silver and grey colors.
    So here are the steps I have taken as to "attempt" to fix the issue  (I have followed these instructions: https://discussions.apple.com/docs/DOC-3353) :
    1. Went into startup manager and ran the disk utility to verify disk volume and permissions. Everything seems to be OK.
    2. Conducted a PRAM reset. No change.
    3. Conducted a SMC reset. No change.
    4. I did a fsck -fy run (in command mode) on startup. No change.
    5. Ran the system in verbose mode and got the following error: "BootCacheControl : Unable to open /var/db/BootCache.playlist"
    6. And lastly, I created 10.8 OSX image on a USB stick and reinstalled ML one more time only to get stuck at the same place yet again.
    Additionally, I can see my computer from my wife's MBP also running ML for a while. The folder that I have set the permission to be available, I can access! I have moved some files, but naturally the files that I want are in folders that have restricted network access. That just tells me the hard itself should be fine (perhaps).
    I am running out of ideas fast to save the system. If anyone can help me, I'd be immensely grateful. Thanks.
    Amir

    Take each of these steps that you haven't already tried. Stop when the problem is resolved.
    Step 1
    The first step in dealing with a boot failure is to secure your data. If you want to preserve the contents of the startup drive, and you don't already have at least one current backup, you must try to back up now, before you do anything else. It may or may not be possible. If you don't care about the data that has changed since your last backup, you can skip this step.
    There are several ways to back up a Mac that is unable to boot. You need an external hard drive to hold the backup data.
    a. Boot into Recovery by holding down the key combination command-R at the startup chime, or from a local Time Machine backup volume (option key at startup.) Release the keys when you see a gray screen with a spinning dial. When the OS X Utilities screen appears, launch Disk Utility and follow the instructions in the support article linked below, under “Instructions for backing up to an external hard disk via Disk Utility.”
    How to back up and restore your files
    b. If you have access to a working Mac, and both it and the non-working Mac have FireWire or Thunderbolt ports, boot the non-working Mac in target disk mode by holding down the key combination command-T at the startup chime. Connect the two Macs with a FireWire or Thunderbolt cable. The internal drive of the machine running in target mode will mount as an external drive on the other machine. Copy the data to another drive. This technique won't work with USB, Ethernet, Wi-Fi, or Bluetooth.
    How to use and troubleshoot FireWire target disk mode
    c. If the internal drive of the non-working Mac is user-replaceable, remove it and mount it in an external enclosure or drive dock. Use another Mac to copy the data.
    Step 2
    Press and hold the power button until the power shuts off. Disconnect all wired peripherals except those needed to boot, and remove all aftermarket expansion cards. Use a different keyboard and/or mouse, if those devices are wired. If you can boot now, one of the devices you disconnected, or a combination of them, is causing the problem. Finding out which one is a process of elimination.
    Before reconnecting an external storage device, make sure that your internal boot volume is selected in the Startup Disk pane of System Preferences.
    Step 3
    Boot in safe mode.* The instructions provided by Apple are as follows:
    Shut down your computer, wait 30 seconds, and then hold down the shift key while pressing the power button.
    When you see the gray Apple logo, release the shift key.
    If you are prompted to log in, type your password, and then hold down the shift key again as you click Log in.
    Safe mode is much slower to boot and run than normal, and some things won’t work at all, including wireless networking on certain Macs.
    The login screen appears even if you usually log in automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.
    *Note: If FileVault is enabled, or if a firmware password is set, or if the boot volume is a software RAID, you can’t boot in safe mode. Post for further instructions.
    When you boot in safe mode, it's normal to see a dark gray progress bar on a light gray background. If the progress bar gets stuck for more than a few minutes, or if the system shuts down automatically while the progress bar is displayed, your boot volume is damaged and the drive is probably malfunctioning. In that case, go to step 5.
    If you can boot and log in now, empty the Trash, and then open the Finder Info window on your boot volume ("Macintosh HD," unless you gave it a different name.) Check that you have at least 9 GB of available space, as shown in the window. If you don't, copy as many files as necessary to another volume (not another folder on the same volume) and delete the originals. Deletion isn't complete until you empty the Trash again. Do this until the available space is more than 9 GB. Then reboot as usual (i.e., not in safe mode.)
    If the boot process hangs again, the problem is likely caused by a third-party system modification that you installed. Post for further instructions.
    Step 4
    Sometimes a boot failure can be resolved by resetting the NVRAM.
    Step 5
    Launch Disk Utility in Recovery mode (see above for instructions.) Select your startup volume, then run Repair Disk. If any problems are found, repeat until clear. If Disk Utility reports that the volume can't be repaired, the drive has malfunctioned and should be replaced. You might choose to tolerate one such malfunction in the life of the drive. In that case, erase the volume and restore from a backup. If the same thing ever happens again, replace the drive immediately.
    This is one of the rare situations in which you should also run Repair Permissions, ignoring the false warnings it produces. Look for the line "Permissions repaired successfully" at the end of the output. Then reboot as usual.
    Step 6
    Boot into Recovery again. When the OS X Utilities screen appears, follow the prompts to reinstall the OS. If your Mac was upgraded from an older version of OS X, you’ll need the Apple ID and password you used to upgrade.
    Note: You need an always-on Ethernet or Wi-Fi connection to the Internet to use Recovery. It won’t work with USB or PPPoE modems, or with proxy servers, or with networks that require a certificate for authentication.
    Step 7
    Repeat step 6, but this time erase the boot volume in Disk Utility before installing. The system should automatically reboot into the Setup Assistant. Follow the prompts to transfer your data from a backup.
    Step 8
    If you get this far, you're probably dealing with a hardware fault. Make a "Genius" appointment at an Apple Store to have the machine tested.

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