Chosen Solution
I’m working on an iMac running High Sierra 10.13.4 that won’t boot. It goes to a gray screen with the Apple logo and a progress bar underneath. The progress bar reaches the end after about 20-30 minutes of booting, but then freezes there indefinitely. I’ve looked online for some solutions and here’s what I’ve found: Reset NVRAMReset PRAMReset SMC (several times)Ran hardware diagnostics - No issues foundBooted into single user mode & ran /sbin/fsck -fy command - first run found & fixed drive errors, second run said it was OKTried to restore from Time Machine - unable to find any restore points.Ran a reinstall of the OS over internet and from USB drive - it seems to have reinstalled OK each time, but after a reboot I get the gray screen with the progress bar again.Tried booting from a USB stick but it keeps saying it is unable to load the OS. Reformatted the USB stick & tried again 3 times with the same result. I’d appreciate any help. Thanks. Update (06/07/2018) Thanks for the input! As it turned out, the issue appeared to be a corrupt OS. I completely formatted my USB drive via the Disk Utility on my other Mac: https://www.howtogeek.com/255251/how-to-… I then downloaded the High Sierra OS from the app store. When that was done, I copied it over and made my USB drive bootable using the command: sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia –volume /Volumes/untitled –applicationpath /Applications/Install\ macOS\ High\ Sierra.app …where “untitled” was the default name given to my USB drive after formatting it. When I tried to do the reinstall from the USB before, I used a 3rd party utility to format & install the OS installation files on the USB drive. Obviously, it didn’t work properly. The reinstall I performed appeared to just fix the OS; it didn’t format the HD & reinstall a fresh copy. Now, I just got a call from the customer again today saying it’s doing the same thing as before. He’s only had it a couple days. I may have to do a full wipe & reload.
Do you have a second Mac which you can connect back to back using Target Disk Mode? How to use target disk mode to move files to another computer After salvaging anything important wipe the drive (reformatting) and reinstall the OS from your other system.
Try Dan’s answer to see it you can extract anything. We’ve been seeing a ton of these in the shop. Most likely your GPU is shot. The 2011 iMacs are notorious for cooked GPU’s. One sure test is to see if your computer will boot to an external drive or Operating system install disk.
