Last week my 2010 Mac Pro running 10.12.3 suddenly started getting stuck booting at the gray Apple logo and progress bar screen. The strange thing is that booting in verbose mode completes as expected. That can be a work around, but I don't trust the stability of the computer if something is getting in the way under normal operation.
Attempted fixes
- Running first aid on the boot disk and rebooting. No change
- Resetting PRAM and SMC. No change
- Wiping the boot drive (data is on a separate drive) and reinstalling macOS. Gets stuck after the installer reboots
- Reseating the drives and CPU tray (along with a cleanup of internal dust). No change
- Swapping out the boot drive with a spare. No change
Best Answer
Not really an answer, but what I'd try next to try to reduce the problem cause further...
This can be tweaked if we get closer to a solution.
Remove all other drives, PCI cards & any external USB devices.
Reduce the RAM to one stick [or one matched pair]
Put the original GPU back, if it's been swapped out [& you still have it]
Boot to Safe Mode [Shift key at the chimes]
If you can get to Safe Mode, make a new admin account & try logging into that.
If possible, set up a known-good boot drive on another Mac Pro & swap it in [This is possible between 3,1 up to 5,1 [I haven't tested other models], a boot drive made on one machine can be swapped directly to another, up to El Capitan but not Sierra]
Test if it can boot from Time Machine directly & if a restore from there works.
Test if it will boot from El Capitan or Yosemite rather than Sierra. I had some odd issues with one El Cap security update which would leave me staring at a white screen & going back to a point before it was my only solution.
Security update 2016-003 10.11.6 issues - which has no real conclusion, just a whole lot of working method. Might be interesting to read if you're bored ;-)