Computer auto-reboots when alt-tabbing/quitting a game

[alphanl]

I've recently been experiencing trouble with my PC. Whenever I alt+tab or quit a game (i.e. Counter-Strike Source), my comp automatically reboots. I've recently installed new RAM and a new video card(Asus AH2600pro). I'll attach the most recent Minidump.

Any help is greatly appreciated.