Mid-2011 iMac won't boot Win 8.1 (BC) w/ ACD 30 attached

I have a 27" mid-2011 iMac Core i7 with two external displays, an ACD 30" and a 20" HP. I spent a great deal of time watching Win 8.1 in a reboot loop after install (Apple Drivers installed fine), sometimes with vertical lines down the ACD 30 (nothing on the HP). (I didnt expect Win to notice the more than one DisplayPort screen.) Finally I disconnected the displays and I booted into 8.1 fine.
IS this a thing? Others share this experience?
Thats not the end of my Boot Camp woes, but that's all tied to this issue.
BP

Can you provide details on how each these displays are connected?
From iMac (27-inch, Mid 2011) - Technical Specifications, you have two TB ports, which can support DP connections.
Please also see
Apple Mini DisplayPort adapters: Frequently asked questions (FAQ) - Apple Support
Target Display Mode: Frequently Asked Questions (FAQ) - Apple Support (this not directly related).

Similar Messages

Mid 2011 iMac won't boot in any mode.

Hello,
Last ast week in the middle of a deadline my imac crashed. I was in the middle of a Pro Tools session and the next thing my mouse icon turns into a series of dots and everything freezes. So, I rebooted and since then I haven't been able to get it to boot in any mode.
On booting it gets to about 1/3 through the progress bar and then hangs.
I have tried the following, all steps have not worked:
Safe Mode
Recovery
Internet Recovery
External Mavericks Drive Boot
Resetting NVRam, PRam
I was able to use target disc mode to get my work from my drives. Randomly it booted once after the crash, I was able to run disc utility's repair disc on my system disc, to which it came back with "disc appears to be fine".
I have taken the iMac to my local authorised service centre, but so far it has been a week and they haven't even looked at it yet.
my question is basically, what could it be that is causing my iMac to do this? I was thinking it may be hardware issues.. But I have no clue really?

*Also,
I have tried running hardware test on startup, but nothing happens when I do. Just stays on the gray screen. After it randomly booted and I ran disc utility, it did the same thing. Mouse icon turned into a series of dots in a vertical line, froze, then rebooted.
After resetting the P and NVRam booting in safe mode shows a blue screen with vertical lines and/or shows some debug info on the gray startup screen.
I will post some photos for reference.

IMAC won't boot with USB card reader attached

My quite new 24" iMAC won't boot if I have a USB card reader attached:
I get to the white screen with the apple logo, but it gets stuck there and the little spinning gear below the apple logo never appears (I've waited several minutes). (In all my test cases, there is no card in the card reader.)
I've tried two different card readers with the same results ("iDOTconnect" brand and a brand new Apacer unit, both are USB2.0 multi-format card readers).
The 1st one I tried via a USB hub, the second one I tried via a new hub and also directly connected to the mac (both of those hubs work fine).
Anyone have any ideas?
Regards,
Strathglass
Message was edited by: strathglass

Hello strathglass
The same thing can also happen with other connected devices such as external HD's and iPods, the Startup Manager is lost and searching for a boot volume.
1. You may be able to fix it by going to: *System Preference / Startup Disk* and select the *Mac OS X 10.5.5 on Macintosh HD* then *Click the lock to prevent further changes.*
2. Leave those devices that cause boot issues disconnected until the iMac is up and running!
3. Only sleep the iMac, and be sure to disconnect those devices be for shutting down or updates that require a restart!
As a habit, I have always ejected and disconnected all mounted USB devices (flash driver, iPods, cameras, card reader, etc.) from my hub be for sleeping, restarting or shutting down...
Dennis

PC Games and peripherals on Windows 7 on Lion on mid-2011 iMac. Possible?

Sorry for the long marquee, but I want to get anecdotal-experience answers on this convoluted subject before I waste a couple months of my fairly-rapidly-closing life --carpe diem. all y'all -- on something that's doomed from the very start.
For reasons I can't quite fathom (relative installed population, maybe), there are very few racing sims -- none, as far as I'm concerned -- for the Mac. That's most def not true for the PC -- I've been a Mac-only user since 1989, but the PC has always been -- when working -- a pretty good gaming platform (ALL it's good for AFAIC), with tons of titles, and the ability to accomodate multi, MULTI-axis controllers, like force-feedback steering wheels with gas, brake, and clutch pedals, and gearshift. I know of nothing like that for the Mac, even if there were racing sims that would run on a Mac.
So here's what I need to know: if I had a Boot Camp partition on my home drive (Macintosh HD), with a 32-bit or 64-bit (full version) of Windows 7 Home Premium, Windows 7 Professional, or Windows 7 Ultimate (necessary for my Mid-2011 27" iMac running Lion or above) installed on that partition, could I then install PC racing sims on that Boot Camp Windows 7-whatever Platform, and be able to use multi-axis controllers, like a Thrustmaster wheel, pedal, and shifter set?
Please, if anyone has been able to do this, by whatever means, on a mid-2011 iMac running OS X 10.7.x or above, I'd be eternally grateful if you could share your experience.
Thanks!
Bart

Seeing as how there are about 117 different versions of 64-bit Windows 7 out there, is there any particular version that is more advantageous -- in the case of Microsoft products, that means less bug-ridden -- for use on Boot Camp? I've seen reasonably priced ($66) versions like this:
"Microsoft Windows 7 Home Premium 64-bit FULL - BRANDED"
But then the description consists of this mangled English:
"This product will be branded HP, Dell, etc. but will do a FULL install on any brand computer and includes a DVD and COA. This is only unique to branded? [sic -- BB] OEM Windows products and not to non branded OEM Windows products. If you are the person people always seem to ask for help when their computer isnt right you should be fine with this. If you are not that kind of user you may want to stick to a non branded oem. Once again this only applies to Mac users [really sic -- BB]."
This is the only part of the description on this product page that even mentions "Mac users," and I'm left wondering if this "FULL - BRANDED" 64-bit version of Windows 7 will work OK on a Boot Camp partition on an OS X 10.7.x -- 10.8.x iMac.
Knowing all too well what a rat's-nest Windows has been since it was first foisted upon an unsuspecting public in 1985, with security problems that, after nearly 30 years, have still not been addressed, I want a 64-bit version of Win 7 that's going to give me the least amount of grief on my Boot Camp partition.
As this thread seems to be pretty much a dead letter, as many discussion threads become after an answer is provided, should I create a new question titled:
"Which 64-bit version of Windows 7 will work best on a Boot Camp partition on an OS X 10.7.x -- 10.8.x iMac?"
Thanks again!
Bart

Cannot upgrade Thunderbolt firmware on mid-2011 iMac

Hi - I'm having problems updating the Thunderbolt firmware on my mid-2011 iMac (21.5").
Can anyone point me to the proper location for this firmware download? I've found several on the site, but none seem to work for me, due to a variety of OS incompatibilities.
For the curious, here's what my system says:
Hardware Overview:
Model Name: iMac
Model Identifier: iMac12,1
Processor Name: Intel Core i5
Processor Speed: 2.7 GHz
Number of Processors: 1
Total Number of Cores: 4
L2 Cache (per Core): 256 KB
L3 Cache: 6 MB
Memory: 12 GB
Boot ROM Version: IM121.0047.B1F
SMC Version (system): 1.71f22
Thunderbolt Bus:
Vendor Name: Apple Inc.
Device Name: iMac
UID: 0x0001000A15928E80
Route String: 0
Firmware Version: d.16 (Eng 1)
Domain UUID: 78CF7309-6B81-CC54-A320-6D5B13722358
Port:
Status: No device connected
Link Status: 0x7
Speed: Up to 10 Gb/s x2
Receptacle: 1
Port Micro Firmware Version: 1.2.1
And here are the error messages from a variety of firmware update locations:
Thunderbolt Firmware Update v1.2
First error: The package was signed with a certificate that has expired (c'mon Apple!)... Do you want to continue with the installation anyway? (yes!)
Second error: Alert: This software is not supported on your system. (any reason why? OS, old other firmware, what?)
I've tried the tricks of PRAM and SMC resets, moved the com.apple.SoftwareUpdate.plist to the desktop and rebooted, etc., etc., but nothing seems to work.
The issue driving this exploration is that the Thunderbolt port appears to be dead - won't support Target Desktop Mode or the Thunderbolt Gigabit Ethernet adapter.
Thanks in advance for any help!

From that very page, it appears that this model does support Target Display Mode - please see the bold text below.
Am I reading it incorrectly?
Thanks for your help here - it's good to have more than 1 set of eyes looking at this!
- Jeff
What are the requirements for TDM?
A Mac notebook or desktop with a Mini DisplayPort or Thunderbolt connection
A Thunderbolt or Mini DisplayPort cable
A supported iMac with OS X 10.6.1 or later. The table below shows iMac computers that support TDM, the required cables, and the port of the computer to which you are connecting the iMac.
iMac Model
Cable Supported
Port on Source Computer
iMac (27-inch Late 2009)
Mini DisplayPort to Mini DisplayPort
Mini DisplayPort or Thunderbolt
iMac (27-inch Mid 2010)
Mini DisplayPort to Mini DisplayPort
Mini DisplayPort or Thunderbolt
iMac (Mid 2011)
Thunderbolt to Thunderbolt
Thunderbolt
iMac (Mid 2012 and later)
Thunderbolt to Thunderbolt
Thunderbolt

I have a 27in mid 2011 iMac and a 2006 mac mini

i have a 27in mid 2011 iMac and i have been given a 2006 mac mini i have no screen to see whats going on on the mini and there is no os onboard how do i get OS X on to the mini so i can get to use this with a tv with hdmi i have the mini dvi to vga connector and a vga to hdmi lead into a samsung 32in led tv, tv keeps saying not connected???

- You said "Apple dvi to via converter with a via to hdmi cable . What is a "via"? I think you mean VGA.
Just what VGA to HDMI cable to you have? VGA is analogue while HDMI is digital. The Mini DVi out is both analogue and digital (DVI-AD). You would need a converter to convert the analogue VGA to digital.
- Yes, when you boot up you should get a chime if the Mac is functional. The chime The sound indicates that diagnostic tests run immediately at startup have found no hardware or fundamental software problems.[1]
http://en.wikipedia.org/wiki/Macintosh_startup
Thus it appears the Mini also has a hardware problem.
Make an appointment at the Genius Bar of an Apple store. It is free.
Apple Retail Store - Genius Bar

How do I restore my 27" mid-2011 iMac EXACTLY the way it was after hard disk replacement?

Hi all.
Recently received an email from Apple saying that the 1TB Seagate hard drive in my 27" mid-2011 iMac is apt to fail anytime. Apparently they used some bad hard drives in the mid-2011 27" iMacs which are problematic so they're offering me a free replacement to a brand new hard drive. I'll be sending in my iMac for the replacement sometime in the next few days.
In preparation for it, I've backed up my entire system using Time Machine into an external harddrive. The backup is up to date & includes all system files. I've also made a Lion install disk on an 8GB USB flash/pen drive using Carbon Copy Cloner.
My question is: When I get my iMac back after the hard disk replacement, will I be able to restore my iMac to EXACTLY the way it was before the replacement using the Time Machine backup & the Lion install disk that I've prepared? When I mean EXACTLY, I do mean EXACTLY, e.g I don't have to re-install all the programs I have, my settings for the programs I have will stay intact, everything is where it should be etc...i.e EXACTLY the way my iMac is right now.
If yes, how do I do it? I've read Pondini's guide: http://pondini.org/TM/14.html
However it is less than clear on certain points, e.g in my case, which one do I have to use to restore my system to the way it was...the Time Machine backups I have on the external HDD or the Lion install disk that I made using Carbon Copy Cloner? And how do I go about doing the restore?
I'd appreciate any & all help given. Thanks in advance!

daniirwan wrote:
baltwo: Thanks for your input! I didn't think of wiping the old HDD before sending it in for the replacement..all those sensitive user data! One question: What's a FWHD?
Already answered. Just note that FW is much faster than USB. See http://help.bombich.com/kb/troubleshooting/how-long-should-the-clone-or-backup-t ake for details.
I already have CCC installed so I'll probably try it out. Are the steps outline here the one that I should do to restore the CCC clone when I get my Mac with the new HDD back? See: http://help.bombich.com/kb/overview/restoring-data-from-your-backup#full_volume_ restore
Yes.
Another question: while I'm booted on the backup/clone, and just after I've wiped the old HDD, how do I reinstall the OS to create a generic user account? Will I have to use a Lion install USB disk?
No. IIRC (if I remember correctly), you can either use a saved Lion installer (hopefully it exists on your backup/clone) or use the Recovery HD. If you have the USB stick w/Lion installer on it, use that.

Re-Installing Snow Leopard on a mid 2011 iMac

I have accidentally wiped the hard drive of a mid 2011 imac 27" there was no install DVD provided for this machine and a retail Snow Leopard disk will not boot, apparently I need 10.6.8 and the retail disk is only 10.6.3 is there any solution to this dilemma?

The machines (we have more then one) all came with SL but no install disks. When I boot with cmd-R it comes up with a globe icon and message - apple.com/support - 6002F. I am now convinced that these machines were so close to the Lion release and were probably intended for Lion but were shipped with SL. I have now tried everthing including Lion install from USB recovery stick created an another SL to Lion machine and this works to the point where after downloading all 3GB of Lion it just goes back to the beginning again! I tried 3 times - good thing we have fast broadband and it failed every time! I then tried restoring a SL and even a Lion clone from another similar Mac but kernel panic every time, tomorrow I will try the retail "Lion on USB" option but it looks like its off for repair as far as this MAC is concerned.

My 2011 IMac will not boot up past the White apple logo screen with the whirly circle

My 2011 IMac will not boot up past the White apple logo screen with the whirly circle. I have tried various commands but to no avail. does anybody have any advice?

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, start up 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 11. 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
If the startup device is an aftermarket SSD, it may need a firmware update and/or a forced "garbage collection." Instructions for doing this with a Crucial-branded SSD were posted here. Some of those instructions may apply to other brands of SSD, but you should check with the vendor's tech support.
Step 10
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 11
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 12
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 13
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.

Apple DVD player not working on Mid 2011 iMac running 10.7.2

I have a 21.5-inch, Mid 2011 iMac which came with Lion preinstalled. When I insert a DVD, Apple's DVD player comes up with the following error:
"A valid video device could not be found for playback. [-70017]"
The DVD player works. I can play DVDs using VLC, and I can use it to burn in iDVD, but Apple's own DVD player simply will not recognize it. I hoped this problem might be solved when I upgraded to 10.7.2, but alas it has not.
Does anyone know how to fix or work around this issue? This computer is used daily for my media-heavy job, so leaving it somewhere for service is not really feasible unless I'm completely unable to work on it.

Please read this whole message before doing anything.
This procedure is a diagnostic test. It won’t solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.
The purpose of this exercise is to determine whether the problem is localized to your user account, or is system-wide. Enable guest logins and log in as Guest. For instructions, launch the System Preferences application, select “Help” from the menu bar, and enter “Set up a guest account” (without the quotes) in the search box.
While logged in as Guest, you won’t have access to any of your personal files or settings. Any application you run will behave as if you were running it for the first time. Don’t be alarmed by this; it’s normal. If you need any passwords or other personal data in order to complete the test, memorize, print, or write them down before you begin.
As Guest, launch the player and test. Same problem(s)?
After testing, log out of the guest account and, in your own account, disable it if you wish. Any files you created in the guest account will be deleted automatically when you log out of it.

I have a mid-2011 iMac running Mavericks. When I click restart the computer goes to a white screen with a spinning circle and does not go any further until I hold down the power button to turn it off. What do I do?

I have a mid-2011 iMac running Mavericks. When I click restart the computer goes to a white screen with a spinning circle and does not go any further until I hold down the power button to turn it off. What do I do?

Ok, sounds like the safe mode boot worked... You probably don't want to always be in safe mode though (some reduced functionality) so does it do a normal boot now? If not, you should then reboot into safe mode and run Disk Utility. Then select Macintosh HD on the left hand side, and click the Verify Disk button. If needed, it will ask you to Repair Disk. If there are errors found, Repair Disk again until there are none. Then try another normal boot and reply with result, wether good or bad.

Cannot get my Samsung SyncMaster S27B370 to connect to my Mid 2011 iMac 27

Cannot get my Samsung SyncMaster S27B370 to connect to my Mid 2011 iMac 27 inch with HDMI to thunderbolt port adapter but works like a charm in Windows 7 when I bootcamp over to it. Any ideas? The cable is working properly as shown by the fact that Windows 7 uses both monitors perfectly. I am using Mac OS X Mountain Lion and have already done the option + cmd + p + r boot reset to no avail. It does not find the second monitor at all as in it doesn't even show up in the display preference pane.

birdmanjay wrote:
... Apple tells me it is the printer mfr issue and printer companies tell me it is apple issue.
Arguably, they're both right.
Changing your router changes everything, so your best course of action is to research the respective printer's documentation and determine how to reset them to factory default condition. Then, add them again using System Preferences > Print & Scan.
For that, I recommend you first "reset the printing system" according to these instructions: Mac OS X: How to reset the printing system. Its instructions for Lion are identical to those for Mountain Lion.
As the article states, it will remove all your existing printers, leaving the Mac's printing system in a similar "factory default" condition ready for you to create a new print queue for each printer, which you should probably do.
Apple's printing support documents contain a great deal of redundancy, but this one may be a good place to start: OS X Mountain Lion: Set up a printer to print wirelessly

My iMac won't boot....Msg says "NO BOOTABLE DEVICE--INSERT BOOT DISK ...

I don't know how to start my iMac up. I don't even know what a boot disk is! Several days ago I tried to run Boot Camp but couldn't continue because I didn't have a Windows program to install si I'm not sure what happened. Can somebody please help me out? Thanks.
Dman- [email protected]

My iMac won't boot....Msg says "NO BOOTABLE DEVICE--INSERT BOOT DISK ...
Posted: Jan 17, 2011 11:44 AM
I'm getting this message again. When I restart using the option key everything is ok. When the computer goes to sleep it has the above message. Is there a setting I need to turn off so this doesn't happen all the time? Thanks.
Dennis

Hi, FaceTime on my mid 2011 iMac running Yosemite 10.10.2.

Hi, FaceTime on my mid 2011 iMac running Yosemite 10.10.2. I have contacts some of which only show option for audio FaceTime, on my iPhone an iPad the same contacts are available for video. Anyone know why, I can video some contacts from my iMac - but not others. The contacts are all synced via iCloud and the audio FaceTime from the iMac works fine to them but the video option is greyed out. If I go to my iPhone or iPad - there they are all ready to receive video. Curious. Anyone have any ideas i have exhausted the web searching.

Please read this whole message before doing anything.
This procedure is a diagnostic test. It won’t solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.
The purpose of this test is to determine whether the problem is localized to your user account. Enable guest logins* and log in as Guest. Don't use the Safari-only “Guest User” login created by “Find My Mac.”
While logged in as Guest, you won’t have access to any of your documents or settings. Applications will behave as if you were running them for the first time. Don’t be alarmed by this behavior; it’s normal. If you need any passwords or other personal data in order to complete the test, memorize, print, or write them down before you begin.
Test while logged in as Guest. Same problem?
After testing, log out of the guest account and, in your own account, disable it if you wish. Any files you created in the guest account will be deleted automatically when you log out of it.
*Note: If you’ve activated “Find My Mac” or FileVault in OS X 10.7 or later, then you can’t enable the Guest account. The "Guest User" login created by "Find My Mac" is not the same. Create a new account in which to test, and delete it, including its home folder, after testing.

Sudden restarts while using bootable USB installer (mid-2011 iMac) - evidence of hardware problem?

Greetings:
For a couple of years I've been suffering from an issue reported in many threads: seemingly random shutdowns and restarts of my mid-2011 iMac. These can happen several times a day, or there can be a gap of weeks between occurences. I've searched the web and discussions.apple.com endlessly, and tried every conceivable solution. I've observed no consistent pre-restart pattern in Console. I've tried removing all unnecessary extensions and start-up programs. Fixed permissions, repaired HDD, many of the diagnostic procedures described by LINC (superuser on this forum). I would sometimes get temporary relief from periodic restart loops, by unplugging the computer and resetting PRAM, but this would not last long. I couldn't discern whether it is a software/conflict issue, or a hardware issue. Have run AHT in extended looping mode, several times, and found nothing wrong. Which caused me to keep thinking it must be a software issue. The last thing I've tried is a clean install of Yosemite, with full HDD erase, from bootable USB.
I did this successfully, restored files from Time Machine...but then a few hours later, a series of sudden restarts began, with 4 or 5 within a couple of hours. I decided to shutdown and restart using the bootable USB installer again, and run Disk Utility from it to check the HDD for errors.
But then, while booted up from the USB (and after running Disk Utility with a normal result): the computer suddenly turned off and restarted! And then it rebooted again into installer mode (i.e. running off the bootable USB), and I ran Disk Utility again and ...it happened again!
So what does this tell me? I am asking all of you for confirmation please. I am thinking this is a strong indication that whatever the issue is causing the restarts, it is hardware based, as the system was running off the bootable USB at the time, NOT using installed operating system or software. AND this reminded me of one other instance where the system had rebooted randomly, while I was in SAFE mode.
Would you agree that this is likely now pointing to a hardware issue? Is power supply the likely culprit? Or?? (and recalling that repeated AHT have showed nothing...). Is it worth trying to fix (out of warranty)?
thanks for any insights,
Warren

These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.
This procedure is a diagnostic test. It makes no changes to your data.
Please triple-click anywhere in the line below on this page to select it:
syslog -k Sender kernel -k Message CSeq 'n Cause: -' | tail | awk '/:/{$4=""; print}' | pbcopy
Copy the selected text to the Clipboard by pressing the key combination command-C.
Launch the built-in Terminal application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid.
Paste into the Terminal window by pressing the key combination command-V. I've tested these instructions only with the Safari web browser. If you use another browser, you may have to press the return key after pasting.
Wait for a new line ending in a dollar sign ($) to appear below what you entered.
The output of the command will be automatically copied to the Clipboard. If the command produced no output, the Clipboard will be empty. Paste into a reply to this message.
The Terminal window doesn't show the output. Please don't copy anything from there.

Mid-2011 iMac won't boot Win 8.1 (BC) w/ ACD 30 attached

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