Advice on graphics card issues

So i have an older machine and trying to run multiple instances of a game called KO. Kept getting a freeze/crashing on one of them when they enter a town or anything with multiple players. *annoying because i have to close all of them and start over when this happens* Ko is a processor intensive game so i decided i would try to do what i could with the proc. I installed a new heatsink/after market cooler. Dropped the temp while playing from about 50c to 38c. Also cleaned up the inside of the machine, had it for years so it's collected quite a bit of dust. Still got the freezing/crashing. So I took the gpu out and it also was pretty nasty. It was runnin at about 63c. blew out the dust and attempted to remove the plastic cover to get to the guts of the card and of course half of the tiny screws are stripped. So cleaned it the best i could. Now it's running at about 50c and still getting the freeze/crashing.

Am i right thinking it's the gpu thats causing this? Does anyone else have any other cleaning tips im missing that might help. I installed an extra fan in the back to pull hot air out *hopefully*. Theres a fan on the side of the case for intake.

Specs:
Amd athlon 64 x2 6000 Windsor
NVIDIA GeForce 9600 GT
4 GB ram
Abit AN9 32x

Would OC'ng the proc help? Or is the machine just to old at this point to do what im asking?

Any help or advice is greatly appreciated. Thanks in advance