My computer has been off for hours. I come home and turn on the computer. But it only comes on for a few seconds and than it just turns off. It powers up for only a few seconds. I don't know what could be causing this. When it's on it works fine. I have a 500 W power supply. I've never had a problem in the past. Sometimes it can take me a few hours of continually trying to turn it on before it actually works. Any thoughts on what could be wrong?