Random videogame crashes?

i had windows xp 64 and almost every game i played (team fortress 2, left 4 dead 2, GTA4, Fallout 3, Oblivion) would always crash randomly. all of a sudden the sound would stutter really fast, like a blue screen of death, but there would be no signal to my monitor. i would just restart every time. i thought it was because xp64 is unstable sometimes, but i reformatted to windows 7 today and left 4 dead 2 still froze. now i know it's probably a hardware issue, but i'm not sure what it could be.