KG7-RAID Problem computer shuts down few second after power up. Please Help!

I'm not sure if this is a motherboard problem or the power supply but
check this out. When I power up my system it turns on and then turn
off a few second later. I normally have to hit the power two or
sometimes three times before the power up "takes". The power supply
is relatively new and everything else works fine. Could it have
something to do with an out of whack power signal telling the power
supply to shut down? The problem is intermittent and I can't reproduce
it on request but it's been happening for about two months now.

I'm running an ATHLON XP 1600+ and Windows XP. Two hard drives 420
watt power supply.

Any help would be appreciated!