Stutter Crash!

so my computer has been consistantly crashing with DX9 games for a while now, im running windows vista ultimate 64x, with 6 Gbs of RAM, this crash is a few mins into the game the screen goes black and my speakers play the last second and a half of audio that was running through it continually until i manually reboot the computer. Commen games this has happened with are dead space, battlefield 2142, half life, half life 2, supreme commander and civ 4, i would really like to play these games again, some i really enjoy…does anyone have any advice? a few things ive ruled out: it is not a power supply problem because it doesnt crash on bbigger games like crysis and DOW2, also it is not a DX driver issue because i just updated those last night, so neither of those, so ya theres my problem, any ideas?