Gforce 6600 PCIe problems in open gl

Hi, I have a problem with all my games that are using openGL. I have all the new versions of drivers from nvidia ( 78.05 forceware ) and when i try to play a game using OpenGL my computer crashes and it doesn`t respond anymore. It appears a black screen or a multicolored screen and the pc does nothing after that and I have to manually restart.
My system is:
AMD 64 3200+
Epox Nforce 4 socket 939 PCIe
Geforce 6600 256 MB RAM PCIe
512 MB RAM
2 S-ata HDD

What OS are you running?
This could be a driver problem, or just hw problem. Hard to say from your description.