At about 320 sec and a temp of 119C it shuts the computer down

Lately I have been having Lock up problems and thought it was the motherboard. Far Cry, Cal Of Duty, and Stalker Clear Skies, will lock, sound loop I have to hard reboot. I thought it was the sound card, it locked up with the motherboard sound and with NO sound LOL! I think I'll pull the 3870 from my other rig for the Game tests!