Startup stops at gray screen
Startup stops at gray screen after gear stops spinning and before log in screen.
I have downloaded new system from recovery disc (Apple web site) and it restarts fine.
I have had to do this 4 times in 3 weeks. Everything has been repaired or checked
with Tech Tool Pro 6 and Disk Utilty. Also, have reset PRAM.
Any ideas?
Mac Pro, OS X Mountain Lion (10.8.2)