I decided to upgrade the stock integrated graphics with geforce 8800gt 512mb from my friend who gave it to me for free. I did some research and I know that the OEM power supply should be able to handle the video card. However, it performs really bad e.g. Counter Strike 1.6 dropping to 40-50 fps ( I have been playing it for years, I know how to set it to 100fps), vertical sync is off and everything. CPU temp is 55+ idle, GPU is 65+ idle. I really looked forward to play newer games on decent settings with the card.
What should I do? Replace the power supply?