Gray screen after installing Yosemite
If you go into the screen that lets you re-download the OS and also gives you the ability to see disk utility command + r during bootup.
Run disk utility and select the Mac Harddriive [not the OS partition] and run the Repair Disk Permissions feature and then restart the computer and you should have a permanent solution to the black/gray screen.
RECAP [make sure computer is off]:
- Turn on Mac
- Hold command + R as system boots up
- When in recovery mode select a Computer Harddriive [not the OS partition]
- Run Repair Disk Permissions
- Reboot
I have a Mac desktop that I updated to Yosemite. After an initial start, it kept going to blank gray screen in the middle of bootup. I have several accounts on this machine. I finally restarted in safe mode and after logging on to my administrative account the Mac informed me I had a piece of incompatible software -- "Instant On". This was automatically moved to the "Incompatible Software" folder and the installation finished. I have done a shutdown and restart and all appears fine.