A computer I built for a friend has started to bo black in the middle of games or other uses. The lights are on, the fans run, but the screne blanks and won't come back on. Won't restart with reset button or power button, don't know if he is holding it down for a while, but only reboots with back power switch. I had him check for bad connections, exchange ram and pull all cards but video and still does it. It's a MSI Pro 2 with an Athlon tbird 650. Could it be the power supply? Any ideas? Thanks