system freeze

I didnt know where to post this..

I am using my old system (4years) for a while because my new one is out of commisson thanks to the power company.

All of a sudden when I go to play a 3D game such as Counter-strike or the such. I only get to play for a little while then my system crashes...

well. The screen goes black like it losed signal, and the Hard drive wont respond to keyboard.

Now I fixed this simply by opening my case. This system has been used as a hard core gaming system since I got it. Always playing. In the last month I upgraded the video card from a TNT2 Ultra to a Geforce 4 ti-4200.

I have check all the fans and they are all clean and blowing/sucking like they always did.. So I am not sure what is at fault.

Help please