iMac won't boot in Safe or Recovery mode, or from startup drive.

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iMac won't boot in Safe or Recovery mode, or from startup drive.

I've done these three startup options several times, but the iMac still freezes on the Apple startup screen. I've zapped the P-RAM, and it still won't boot in any mode. If I use an external flash drive with a startup High Sierra, it still freezes on the gray Apple screen, about 1/5 the way in, consistently. Clearly there's a problem, but I can't seem to get past the frozen start-up. Yesterday the computer shut down by itself while playing a YouTube video that stuttered and blinked, then died. Haven't been able to startup fully since then, so I cannot access Disk Utility or Terminal. Any ideas? Thanks.

iMac Line (2012 and Later)

Posted on Jan 13, 2020 11:16 AM

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Answer 1

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HWTech

Level 9

60,482 points

Jan 14, 2020 9:24 AM in response to gkgraphics

A 2008 iMac can only go up to macOS 10.11 El Capitan.

For a system this old I would suspect a failing hard drive.

You can try installing macOS to an external USB drive to test the theory. Even installing to a USB stick would work although it will run extremely slow.

You can also create a Knoppix Linux USB drive using Etcher (Mac/Windows/Linux). Option Boot the USB drive and select the orange icon labeled "EFI". While Knoppix is booting it may appear that the iMac is frozen on the Apple boot picker menu so give it lots of time to boot (Its a Mac thing, plus some USB sticks are slow and a failing drive can slow a system). Use Knoppix version 8.2 since I've encountered some odd video issues with the more recent v8.6 release.

If Knoppix boots to the Knoppix desktop it likely means the main iMac hardware is Ok and you have a failing hard drive. You can check the health of the hard drive by clicking on the Knoppix "Start" menu in the lower left of the Taskbar and navigating to "System Tools --> GSmartControl". Within the GSmartControl app double-click on the iMac hard drive which will open the health report for the drive. Post the complete report here so I can evaluate the health of the hard drive.

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Answer 2

HWTech

Level 9

60,482 points

Jan 13, 2020 9:54 PM in response to gkgraphics

What is the exact model of your iMac? You can get this information by entering your serial number here or here.

See if you can run the Apple Diagnostics.

Have you modified or otherwise upgraded the iMac?

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Answer 3

gkgraphics Author

Level 1

63 points

Jan 14, 2020 7:14 AM in response to HWTech

This is an old iMac (24-inch, Early 2008). It was customized at purchase with a 750GB Serial ATA Drive, but has not been otherwise modified, and I can't recall which OS it's running, but I think it's High Sierra. It might be Yosemite. In either case, I tried to reinstall the OS, both Yosemite and High Sierra, and though it would boot using the thumb drive, it would not install either OS—gave me a gray violator symbol on a white background, with no option to do anything other than shut down manually.

I did try running Apple Diagnostics, but I still get only the white screen + Apple logo and progress bar that hangs at about 1/5 in. In other words, it refuses to run the diagnostic. I fear this is not good news.

Thanks for any help you can offer.

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Answer 4

gkgraphics Author

Level 1

63 points

Jan 14, 2020 11:13 AM in response to HWTech

Well. I took it to the shop and the hard drive is kaput. No surprise with an iMac of this age. Now I can get a solid state Mac! But sigh. Thank you for your help. Much appreciated.

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iMac won't boot in Safe or Recovery mode, or from startup drive.

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