Computer just rebooted and I got this message. opt temp3 overheat protection. . Could anyone explain this to me?

I am also getting randon crashes when I exit Enemy Territory game.

I ran memtest for 12 hours no errors. Thanks for any help.

quad 6600
maximus formula bios 802
g Skill MEM 2Gx2|GKS F2-8000CL5D-4GBPQ R
msi raedon 3870
coolmaster 750 power supply
cosmo 1000 case