Gaming computer crashing 2-3 months after new video card is installed?

I have an older gaming computer (2007-2008) that goes through odd cycles of crashing during intense gameplay. The computer suddenly and without warning turns off as if someone pulled the power cord out of the wall (it does NOT just restart or reboot). To fix the problem I have found that replacing the computer's video card (currently a nVidia 9600GSO) will stop the shut-downs for a 2-3 month period, but then it begins to happen again. The computer does not seem to get over heated and the PSU is strong enough to support the older video cards I use. Does anybody else have any experience with problems like this? Would anyone know how to fix this issue?|||You can't just upgrade the video card on a piece of crap computer and expect it to turn into a gaming one!|||Hello,



1. What kind of powersupply do you have?

2. What card did you upgrade to?

3. How are your temps in-game?