A mate of mine's PC keeps randomingly turning itself off. No errors, no blue screens and the odd thing is, it wont turn back on unless you plug it into a different power outlet. It hasnt blown the original outlet our fuse either, because it will work again if you try it after ten mins or so.

Replaced power supply, but to no avail. I'm thinking motherboard, but I dont particularly want to order one without being completely sure its that. So, any other suggestions? Very simple set up, Asus motherboard, Athlon XP cpu, 512mb, bog standard nvdia FX card.