I restarted my macbook pro this morning and it started up with a chime and now is stuck on the grey screen. I have tries holding any different key combinations, none of them work, except resetting the pram, which does cause the computer to restart.
I have tried option, r, s, d, command shift v, command v, shift (before and after the chime), command option d r.
FYI I have been running yosemitr for a while with no problems. I shut my computer last night and it was working fine. This happened when I turned it on today.
Best Answer
Disconnect everything from the Mac and then power it off.
Perform recovery according to these steps.
If that fails, then you may need support from Apple to determine the version of OS X that shipped with the Mac so you can restore that and start over/restore from a backup once the hardware is known to work. Or it needs a repair for hardware issues.