Wierd problem with cracked games

[Enfurno]

Hello all, im having the wierdest problem, any gmaes i have that are cracked will play just find for oh roughly 5 - 10 minutes, then the screen will go all wierd looking like some sort of plaid design and freeze up the pc, i have adjusted refresh rates, tried different cracks, im having this problem with
rise of nations
generals:: zero hour
and freedom fighters.

anyone have a clue?

btw im running a gforce fx 5200 ultra
53.03
DX 9.0b