I took the side of the computer off and stuck an external house fan right next to it and itll stay on longer... i think the record is maybe an hour tops but its slowly gotten worse.
I have a Saphire ATI Radeon HD 4650 1gb DDR2 in there as an upgrade that i did about a year ago.
Idk what else it would be besides the graphics card. the on board graphics card already went on this pc cus screen wouldn't turn on until i switched plugs and plugged monitors into the add on 1gb card. worked great for 6 months or so but now thats turning off too.