I actually have this exact same problem and am also looking for a solution. I'm running Vista, with a new Coolmax psu, a new bioware mobo, new buffalo ram and a new AMD processor. My situation is the same though. It will just off at random and the only way to turn it back on is to unplug the psu and plug it back in. At times it will stay on for hours/days, others for less than a minute. I'm getting ready to run the memory test that was suggested, but I haven't really figured anything out yet. Any advice would be greatly appreciated. Thanks in advance.