Dolphin, the GameCube and Wii emulator - Forums

It´s quite possible that
1. Either your hardware CPU, GPU or RAM is failing
2. You have high temperatures causing your CPU to throttle

Its likely that it's the 2nd possibility. But we need more information.
Taking Dolphin games and those PC games you mentioned, do both of them just freeze every few minutes but stay playable? Or do you crash? (Blackscreen, BSOD, audio loops, display turns off)

It can't hurt to monitor your temps already either. Get a temperature monitoring application such as CoreTemp and check what your temperatures are on idle and when playing your games.

no i dont think its any of those problems cause i just bought my PC 2 weeks ago and i have 5 fans in it

in windows 7 i get a black screen for 2 seconds and then i get an error that my nvidia drivers crashed
in windows xp the games freeze every fews seconds but stay playable and i dont get any error for the drivers

It doesn't matter if you bought your pc a day ago or not. There's always a chance the hardware you bought was damaged during manufactory or shipment etc.
Just check your temps etc, test your memory and see if that's the problem or not.
There's just too many things to go through, but if you don't cooperate, we can't help.