Computer crash, random colored dots and weird sounds.

[Paprika]

When i'm playing games, or watching HD videos sometimes (not always) My pc freezes, starts looping random sounds and shows colored dots. I used to have this, than i reinstalled windows. Which didnt do anything, then i reinstalled it again and somehow i didnt get the crashes anymore for about 3 months. But now i'm getting them again. I've got a 9800GT 512mb green card from palit. And an ASUS P5G41-M LX for the motherboard. Intel Dual Core 3Ghz and 4 gb of DDR2 memory. GFX card idles at around 40 and when gaming at about 50/60.

 

[Paprika]

45 idle and about 55 on load