Hmm, must be too early... I suddenly remembered a situation like this I
had with a motherboard a few years back...
check the ISA slots; make sure nobody's stuck a card in there and
mangled a few of the pins. This board I was given had the same trouble,
and a couple of the pins were shorting out and the system was shutting
it down. Nice three-second fix once I'd found the problem!! :)