Usually if the computer starts and within a minute it shuts off you have a hardware problem. This is usually a heat problem. Are all the fans running? do any stop after a few minutes? First thing to do is reseat the processor heatsink with some good thermal grease to make sure the processor is NOT overheating. Most newer motherboards have a sensor that shuts down the motherboard when temps get past a point set in the bios? It sounds like the computer is staying on for more than a minute or two. Do you get a POST BEEP? When the puter shuts off it would be a good time to check the chipsets and processor heatsink to see how hot they are. Don't grab on or even touch the areas, just hold the back of your fingers very close to see if you feel any heat. Normal temp should be close to 105-110° F for the processor. If it seems to be very hot then it probably is. Chipsets run about the same temp. Set a floor fan blowing at full speed into the open side of the case( after taking the side cover off) and see if the computer stays running any longer. If that doesnt help then you have some damaged hardware that needs replacing. Thats what a good computer shop is used for. I charge very cheaply to this kind of stuff because it always brings people back in for other things. I may only make $20 finding the problem but people remember that and come see me when they want to upgrade. So you may want to try finding a local shop that will not charge very much just to look at your computer. They can find the problem much faster and easier than you can since they normally have some spare parts lying around just for such occasions. I know i do. Thats why i will save old working computers for when i need a test part.