Go to Tigerdirect.com What you have going on is either Over heating of the processor and it is shutting down or the power supply is going bad. Or maybe a short in the Mother board.
1. If your getting a Bios and you have reformatted the drive and still shutting down that it sounds like eith a power suppy or bad motherboard. or processor.
At Tiger they have combows of mother board and processors or Kits with almost everything in it. Here is phily A local place I just got an asus board and Amd 3000 processor and fan for around 200 and i just replaced the old board and placed all the cards back in . Installed Xp on it and it worked fine.
Good Luck with YOUR Mother inlaw
I think it is your mother Inlaw
anyways Good Luck