I think it's the power supply. These are easy to replace. Remove 4 screws and unplug all the old cables (2 of them will have little thingies on the side of the plug that you need to press to remove it from the motherboard sockets). Pick up a 400+ watt one at Fry's. If you're not sure what to get, take the old one with you. A motivated user can replace one in under 10 minutes for around 50 bucks.