I have a 4870 ATI ox black edition, and it used to work fine but lately my computer has been restarting unexpectedly during game play. I took a look at GPU activity and it was off the roof.. 99% just at the menu of crysis, and 50-99% during gameplay of almost any game.
With GPU activity increase comes temperature increase and that is probably why the computer would restart. I tried reinstalling the drivers but I got an error that said "Zero Display Service Error"... which really seemed weird because it didn't effect my normal installation and I can still play games like Elder Scrolls IV Oblivion at 35% GPU activity.
Edit: Woah weird.. I read somewhere that if you standby and log back in, it fixes the problem. I just tried this and it worked! I play crysis at 0% activity now and my card temperature doesn't even increase..
I do not know if this is just a temporary fix, however. (i am saying this to help others with the same problem and I want your take on this or if anyone has found a different, less weird fix)