Updated to Tiger, stuck on grey screen BUT boots fine with option key

I've searched the forum and found many other similar threads. But no real answers for my particular problem. Here it is. iMac 800 MHz G4, 512 RAM was on 10.3.9. Updated to 10.4.5. Then booted from a firewire hard drive and fixed permissions and ran Disk Warrior. Now when I try to boot up normally it just stays on a blank grey screen. No Apple logo. No spinning wheel, nothing. Weird thing is it boots up fine if I hold down the option key at start up and select the hard drive. So, I've done that and repaired permissions and run disk utility. Says everything is OK. Even zapped the PRAM. But still, only way to get it to boot is by holding option key and choosing hard drive. Any ideas?

Hi Steve, What other start up options are you seeing when you boot with the 'Option' key? Have you tried a 'Safe Boot"? Hold down the 'Shift' key while restarting until (hopefully) you see the spinning gear wheel. Wait while it restarts, this takes a lot longer. If you can boot into 'Safe mode' then in System Preferences>System>Start up disk, make sure that your hard drive is selected.
If you can't boot into 'Safe mode' (you should be able to) then when you have booted with the 'Option' key, follow the 'System Preferences' advice above. Select your hard drive & 'Restart'.
Also have a look at
Dr Smoke's Troubleshooting Startup and Login Items.
For future reference, bookmark his X-Lab home page. There is a wealth of helpful information. Obviously he'd like you buy his 'Troubleshooting' e-Book, but there's loads there for free.
As Dr Smoke would say: "Good luck! "
Have fun too!
An  a day...
Adrian
ibook G4: 768mb, iMac 17" G4:768mb (10.3.9) Mac OS X (10.4.4) Belkin Wireless F5D7632

Similar Messages

TS2570 My Mac is stuck on grey screen what's wrong with it and am I going to lose everything

My Mac is stuck on grey screen what's wrong with it and am I going to lose everything

Hopefully you have a backup, but...
Could be many things, we should start with this...
"Try Disk Utility
1. Insert the Mac OS X Install disc, then restart the computer while holding the C key.
2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu at top of the screen. (In Mac OS X 10.4 or later, you must select your language first.)
*Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.*
3. Click the First Aid tab.
4. Select your Mac OS X volume.
5. Click Repair Disk, (not Repair Permissions). Disk Utility checks and repairs the disk."
http://docs.info.apple.com/article.html?artnum=106214
Then try a Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes.
(Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive.)
If perchance you can't find your install Disc, at least try it from the Safe Boot part onward.

My old mac powerbook g4 wont boot up, it wont show apple logo and spinner aswell just stuck on grey screen while booting please help me

i have a old powerbook g4 which i usally use to store some photos and to listen music. the battery of my powerbook is completly dead so i used to use my powerbook using charger adapter so whenever my power cuts down my laptop will be shutdown.
one day i had just bootedup my powerbook and some date notificateion poped up so i press enter and suddenly my power went off and laptop shuted down. and next time when i tried to boot its stuck at grey screen , i even cant reach the apple logo and spinner. please helppp me :!!!!!!!!!!!!!!!

Resetting PRAM and NVRAM is not working
and i cann't boot it on safemode holding shift button and while holding option or c button at startup i can only see three things 1 is refresh button, 2 macintosh HD with X under it, 3 arrow forward button please help me

Macbook does not boot. stuck at grey screen. have tried single user mode, but text stops at AppleIntelCPUPPowerManagement: initialization complete, without anymore prompts. no

macbook does not boot. stuck at grey screen. have tried single user mode, but text stops at AppleIntelCPUPPowerManagement: initialization complete, without anymore prompts. no hash key appears that will allow me to type in: fsck -fy
have my trials for IB in one week and my history notes are all on my hard drive, that has not been backed up. help please =(

macbook does not boot. stuck at grey screen. have tried single user mode, but text stops at AppleIntelCPUPPowerManagement: initialization complete, without anymore prompts. no hash key appears that will allow me to type in: fsck -fy
have my trials for IB in one week and my history notes are all on my hard drive, that has not been backed up. help please =(

My MBA now just goes to the apple logo on the grey screen but no further

My MBA now just goes to the apple logo on the grey screen but no further... I did some updates on Office but it did not freeze on install and recently I installed Joost.
I thought about booting it from a disc but now I have a disk stuck in my MAB superdrive that I can't get out since at this stage it will not eject... it is a mess...
I am new to Mac, so I am lost...
Anybody can help me with tips ?

Installed Acrobat Reader for Mac. Rebooted and get apple logo, grey screen and perpetual blue screen, no further. I have dual systems installed and can boot Windows XP Pro with no problem so it appears to be a Mac OS problem, not hardware. Awaiting help.
_*WARNING to others who may have same problem installing Adobe Acrobat Reader and Office updates (see germmac post).*_

Macbook pro retina 2012 mid year stuck on grey screen

Hi everyone.
I've just update for the lastest mac os x mountain lion update, when half way the progress and it goes stucked. All the function are unable to function, so i've force shut it down. After mac shutted down and i tried to boots it back it stuck on grey screen which below apple logo forever loading icon. i've tried Reset the PRAM, but it still not working for me. Also, i tried when when start up hold with cmd + r to reinstall the os x , but it just won't let me to reinstall it , it wrote you can't upgrade this version of OS X because a newer version is installed?
Help please! need a solution that wont delete all my files at the same time

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 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.”
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. Use the working Mac to 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. Note: If FileVault is enabled on some models, or if a firmware password is set, or if the boot volume is a software RAID, you can’t do this. Post for further instructions.
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.
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 corrupt 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
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.
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 Time Machine or other backup.
Step 8
This step applies only to older Macs (not current models) that have a logic-board ("PRAM") battery. Both desktop and portable Macs used to have such a battery. The logic-board battery is separate from the main battery of a portable. A dead logic-board battery 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. You may have to take the machine to a service provider to have the battery replaced.
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. If you can't get to an Apple Store, go to another authorized service provider.

10.6 won't boot; stuck on grey screen

I know this is covered here to some degree, at least, but I haven't been able to find a complete solution/answer, so here goes:
(Please, redirect me to the right source of information, if you know where to look, but not before reading through my post. Thanks! Oh, and I'm no computer expert, so, please, bear with me.)
First of all, my equipment: 17" iMac (serial #: w86262cru2n, emc #: 2104), running (ran?) 10.6 (w/updates)
So, as my title says, my iMac won't boot up and gets stuck on the grey startup screen with the  and the spinning wheel. I can wait and wait, but it never gets past this point.
Here are some things I've tried (nothing has worked so far; "no success" = stuck on grey screen). These steps are also laid out here.
- Tried normal startup (no success)
- Tried Safe Boot (no success)
- Tried booting without connected peripherals (no success)
- Tried alternate outlet (power source) (no success)
- Tried resetting PRAM & NVRAM (no success)
- Tried boot from 10.6 Install Disk (no success)
- Tried replacing original RAM (no success)
- Tried mounting internal drive as Target Disk on my 10.5 MacBook (mounts fine; used 10.6 install disk to verify, says disk is "ok")
- Tried booting to MacBook via Target Disk (i.e. iMac is external drive connected by FireWire) (no success)
- Tried booting from cloned copy of 10.6 disk on an external USB drive (yes, this can be done; I've done it before). This drive was verified "ok" in the same way the internal disk was (see above). (no success)
My next step appears to be to erase the original internal HD and reinstall 10.6. This is where my my ignorance begins to rear it's head. Since I can seem to boot from the iMac, can I do this through my MacBook, viz. mount the original, internal, 10.6 disk on my MacBook and erase it and install 10.6 from there (e.g. through Disk Utility on the 10.5 MacBook)?
Assuming this is possible, can someone step me through the process?
Assuming this last step isn't possible, does this all point to a faulty logic board (sounds like a 'worst case' to me)?
Any ideas? Suggestions?
Many, many thanks, BTW, to all who have posted here and whose help I've availed myself of anonymously many times. And thanks in advance to anyone with helpful ideas.

Try a SMC reset and follow the steps again in the support doc for grey screen
https://support.apple.com/kb/ht3964
https://support.apple.com/kb/TS2570
Your 10.6 install disk seems unreadable if it won't "hold c or option" boot.
Clean the bottom with a alcohol and a very soft cloth and lightly polish until there is no streaks.
Don't touch the bottom or place the disk onto something that will mar the bottom.
If the disk still fails to work, get a replacement, as your going to need it. Get a jeweled plastic case for it.
To make copies of your Snow Leopard install disk, follow these directions.
http://www.walterjessen.com/make-a-bootable-backup-snow-leopard-install-disc/
Once you can hold c and boot off a working 10.6 install disk, simply reinstall OS X without using Disk Utility to Erase and Format the drive, this will replace the OS X installed (and bundled programs) with the disk versions, then reboot and immediately use Software Update to get current.
Your user files, third party programs will remain untouched, except for ones installed in OS X/root system files, those will have to be reinstalled with updated copies.
All else fails:
Grab a copy of your recent user file folders via FireWire target disk mode first or from a hold option bootable clone on a external drive
If you have to completely erase and reformat the drive, reinstall 10.6, there are some things you need to know.
1: The free iLife that came with your 10.5 install disks are not on the 10.6 retail disks
So to get that you need to select the drive makers name in Disk Utility, erase and install with the 10.5 disks first (warning, wipe entire drive)
2: Name the boot drive the same name as before in Disk Utility when formatting.
3: When you go through inital "Welcome to Mac" setup, use the same username as before, (different password)
4: Once in OS X 10.5 stick a working 10.6 installer disk in and upgrade. Once rebooted, immediately Software Update to current version.
5: Install programs from fresh sources next and update.
6: Finally, return the backup copies of your user file folders (Music, Documents, Pictures, etc., not Library) to their respective folders on the new configuration. Because you used the same hard drive and user name as before you should have little complications with things like iTunes song locations/playlists and other hard references to files on your drive.
By installing the OS first, then upgrading, then programs, then finally user files last, keeps the drive optimized as the drive is faster on the data installed first than data installed later. Since users files change size often, having them towards the end where they can grow or shrink keeps the performance of the computer up as much as possible for the OS and applicaitons. Eventually though with OS X updates it can get a bit more defragmented, but not much.

Macbook pro model A1278 wont boot osx stuck at grey screen

I have had my mbp for about 3 years now and has worked great. Just today i got home from work and when i opened the macbook which was already running I was in OSX but it was frozen with colored wheel spinning. I had never experiened this before but I didnt think too much of it and held down the power button to reset it. Now i am stuck at the grey screen with the Apple Logo and spinning wheel and cant get back into OSX at all. So i started googling (on another computer obviously) and tried:
1. boot in safe mode. Didnt work, still stuck at grey screen
2. boot in safe mode with "commd-shift-v" to see info. stuck in "dos" looking screen. see pic at bottom.
3. tried resetting VRAM w/ "commd-opt-p-r". did not work, still stuck at grey screen.
4. got original OSX install DVD. Was able to boot to disc and make it to disk utilities. went to repair and got error "unable to unmount disk"
5. ran "repair permissions" and completed that. ran "verify disk" and got green "disk ok" message. then re-ran repair and got same "unable to unmount disk"
so know i am worried. my main concern is the 80 GB of music I have on this computer (and dont currently have backed-up {que back-up lectures}) and my pictures. Does it sound possible to recover music and pics based on this little bit of info? Im willing to take it to the Apple store and pay the price if it sounds like I can recover it. I am pretty computer savy but am reluctanct to just start trying anything that could lose my music/pics. I cant try just deleteing and restoring OSX to factory settings and losing all that music/pics.
so...what is best approach to access and back up these files myself? I do have another macbook with a firewire connection but am not familiar with that process. I will get a external HD immediatly (now ofcourse)...can I backup my files from disc utility?
Thanks for any help.

Sorry about specs...i entered in drop box menu but realize doesnt show on thread:
MacBook Pro "Core 2 Duo" 2.53 13" (SD/FW)
2.53 GHz Core 2 Duo (P8700)
Intro Date:
June 8, 2009
Disc Date:
April 13, 2010
Order No:
MB991LL/A
Model No:
A1278 (EMC 2326*)
Subfamily:
Mid-2009 13"
Model ID:
MacBookPro5,5
Std RAM:
4 GB
Std VRAM:
256 MB
Std Storage:
250 GB (5400 RPM)
Std Optical:
8X DL "SuperDrive"
I was running the last vesion of snow leopard (10.6.8 i think).
I picked up a firewire today and am going to attempt to make "broken" macbook target and pull files onto other macbook. Will give an update tomorrow after attempt. Thank you for fast response.

Need Help For iMac G5 Stuck On Grey Screen Or Apple Logo No Spinning Gear!

Hello everyone i'm new here and i'm new for using iMac for some reason i was trying to clean or to fresh installation the iMac that my brother gave it to me that he bought it into the flea market without the original disk on it! when i erase the Macintosh HD and some of the partition o iMac then reboot it now the iMac stuck on grey screen or apple logo no spinning wheel shown. and i also try to search and try all the tips of all mac user's like all the command key's and follow the instruction of them but still nothing happen..
Holding CMD & R just to go disk utilities nothing shown up only apple logo and the noisy fan.
Holding alt and it go to blue screen and show my mouse Pointer Refresh Logo, Hard drive Icon, Arrow Sign.
i can click Arrow Sign and it go Apple Logo and within 2-3 seconds and it change to Power Sign Logo,
i can click Refresh Logo but nothing happen .
i can't click the Hard Drive icon.
CMD, Option, P & R to Reset i also try and it's the same nothing change.
CMD, Option, ESC no action shown.
Is there anyway to fix this issue or problem please and thank you for help.
Hoping to get result for all of you guys P.S
iMac G5
v10.5.8
Leopard

You need to have the install DVD that was issued with the iMac
You can call Apple at 1-800-275-2273

Powermac G5 stuck on grey screen start up and fans running wild

Hi All
I also have the recurring problem all of a sudden - yesterday all seems well, today am stuck on grey screen and fans getting stronger by the minute. NOTHING works - have been through all sorts of forums and the most I got was to try disk utility - which says all is well - replaced the battery - tried just about anything short of pouring some acid on the **** thing, won't boot from original install CD either - I really need this machine as I earn my living with it and cant afford a new one and why as it was working just perfect - now this mess. In a way don't know why the excellerating fans are not built to simply pick up speed and then eat into the PC board and CPU - at lest this way we know for sure there is nothing we can do.
Does no one here know why the mac is doing this - not even the mac fundies? Unbelievable. I live in Namibia and Apple Mac support here is similar to that on this website - might as well write this on a wall - that is why I am really frustrated... **** Mac

Follow these steps in order:
http://support.apple.com/kb/TS2570
The G5 is also subject to solder failure around the RAM slots and memory controller.
It is a fatal condition, but one that can sometimes be temporarily sidestepped by heating the logic board between the RAM slots with a hair dryer.
Heat the board until very warm (hot) then start.
If your machine starts after heating, then you better just leave the machine on all the time.
You never know when the trick won't work......

Stuck on Grey Screen During Startup

I updated to Yosemite on Saturday and everything has been working fine, I have been able to shut down and startup as normal until today.
Last night I forced my Early 2011 MacBook Pro to shut down and today it will no longer get to the login screen.
I hear the chime, the Apple appears with the Yosemite status bar underneath, it takes a long time to get about halfway then both the Apple and status bar disappear leaving just a blank grey screen.
- I can get into Single User mode, using "fsck -fy" it reports that everything is OK.
- I can't get into Safe Mode.
- I have reset PRAM
- I have NOT reset SMC (is it worth a try?)
- I have a bootable Yosemite USB, holding option I can select that but instead of presenting the Utilities window it just brings up the Apple and status bar then grey screen. For some reason my WiFi network isn't in the list either. Also, the image of my hard drive that appears has a custom icon that I haven't used for at least 5 years, very odd indeed.
I'm at a loss, any help would be greatly appreciated.
NOTE
My left fan is faulty, I have ordered a new one online. I have been using SMCFanControl to monitor it, if the computer has been feeling hot I have been increasing the RPM for a minute to cool it just to be safe until the new fan arrives. Last night I increased the RPM and SMCFanControl became unresponsive which is why I forced the computer to shut down because I couldn't reduce the fan speed back to normal.

I am able to get into Internet Recovery Mode but eventually the globe disappears and it's right back to the Apple and status bar then grey screen again.
When holding Option only my hard drive shows, there is no recovery drive option.

Stuck on grey screen screen at start up...apparent Qmaster bug.

So I found what appears to be a bug. At least for me...and at least in 10.6. Not sure if this effects other OS versions.
I was having an issue with start up getting stuck on grey screen. Symptom is eventually start-up circle segments would stop spinning and left hanging there on the grey screen.
There are Apple doc's and ample google hits on this subject. But I have found nothing pertaining to Qmaster as being a possible cause.
It took me awhile to figure it out and was not an obvious issue.
I thought it might be helpful posting this here to bring this up on a google search for someone who may be having the same problem.
My issue:
Doing image sequence Maya render's. However, I doubt it is Maya related.
If I pause the render in the Batch Monitor. And shutdown. Something with Qmaster still being active hangs my startup. It is repeatable behavior.
I have to start up holding shift key for safe mode.
You will note, if you have 'Show Qmaster service status in menu bar', under the Advance button of QM's System Pref's pane, that the green light is on.
That green light being on, gave me the clue that it was something to do with Qmaster.
Clicking; Stop Sharing and restarting clears the start up hang.
It appears, whatever permutations Qmaster expresses with a paused render on start up, is somehow preventing normal start up.
Since I have read that menu bar items may be one possible cause for start up issues. It's also possible and therefore worth mentioning that unchecking "Show Qmaster service status in menu bar". May also resolve the problem. I have not tested that.

Issues like this are often caused by startup jobs that are taking far too long to finish. It definitely looks like a serious bug so it's worth reporting it to Apple at either of the following places:
http://www.apple.com/feedback/compressor.html
http://bugreport.apple.com

STUCK ON GREY SCREEN! !PLEASE HELP!

!!HELP!! STUCK ON GREY SCREEN
I have a MacBook 10.5. Its a few years old anyway it seemed to be working fine up until a couple of weeks ago then it started taking ages to startup.
I started it in singlemode then typed /sbin/fsck -fy then a message came up "harddrive appears to be ok" next i typed "reboot" and the system started booting.It started as normal with the apple logo and spinning chime,next the screen turns blue where the login screen normally appears but then the screen turns grey with no logo with just the pointer arrow on it and it doesn't seem to load past that point.Can anybody please help me solve this problem i have my kids photos and stuff on it that are unreplaceable.
Hopefully there's a command line that can help also I don't have a installation disk so is there a way I can download 1 onto USB??
THANKS HEAPS!!!!!

Hi Eug07349,
Thanks for visiting Apple Support Communities.
It sounds like you may be experiencing a software issue. I'd suggest trying the first two steps in this article (Disconnect, test peripheral devices and network cables, Perform a Safe Boot):
Mac OS X: Gray screen appears during startup
http://support.apple.com/kb/ts2570
Best,
Jeremy

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.

MacBook Pro stuck at grey screen after Yosemite upgrade

upgraded to yosemite yesterday. Reboot and stuck at grey screen(login in page) when i log in there is some codes thing at the left top corner of the screen. and then it reboots again. Which means I can never log onto the computer. what should I do

If you can't start up and log in in the usual way, try in safe mode.
During startup, you’ll see a progress bar, and then the login screen, which appears even if you normally 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.
Log in as an administrator to carry out these instructions. If you have only one account, you are the administrator.
☞ If you don't see any reports listed, but you know there was a panic, you may have chosen Diagnostic and Usage Messages from the log list. Choose DIAGNOSTIC AND USAGE INFORMATION instead.
Safe mode is slower than normal, and some things won’t work at all.
Note: If FileVault is enabled, or if a firmware password is set, or if the startup volume is a software RAID, you can’t start in safe mode.
If you're able to log in, launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Console in the icon grid.
In the Console window, select
DIAGNOSTIC AND USAGE INFORMATION ▹ System Diagnostic Reports
(not Diagnostic and Usage Messages) from the log list on the left. If you don't see that list, select
View ▹ Show Log List
from the menu bar.
There is a disclosure triangle to the left of the list item. If the triangle is pointing to the right, click it so that it points down. You'll see a list of reports. A panic report has a name that begins with "Kernel" and ends in ".panic". Select the most recent one. The contents of the report will appear on the right. Use copy and paste to post the entire contents—the text, not a screenshot.
I know the report is long, maybe several hundred lines. Please post all of it anyway.
In the interest of privacy, I suggest that, before posting, you edit out the “Anonymous UUID,” a long string of letters, numbers, and dashes in the header of the report, if it’s present (it may not be.)
Please don’t post other kinds of diagnostic report.

Updated to Tiger, stuck on grey screen BUT boots fine with option key

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