OS X 10.10.2 Grey screen and progress bar at start-up normal?
I'd run the 'usual suspects' before anything else. 

Disk Utility > check/repair disk. 

Then get OnyX (free/donationwear) &amp; reset ACLs (Maintenance tab > permissions, check the box at the top.)  

Then re-apply the 10.10.2 combo update.