Strange phenomenon

I turned my computer on today after it had been off for 2 days (it usually
runs 24/7 so I thot I'd give it a break) and when I did the strangest thing
happened. It turned itself on and off rapidly on off on off on off like a
light bulb. I had to kill the power from the rear switch to stop it. this
happened 3x in a row then the 4th time it came on and seems to be working
fine thus far. I'm thinking maybe the power supply or the power circuit on
the mobo? any ideas greatly appreciated. I'm afraid of what might happen the
next time its turned off or a power outage occurs.. Thanks again

Gigabyte GA-K8NS Ultra-939 mobo
Athlon 64 4000+
2GB OCZ rev 1 ram (4x 512)
ATI X800XT all in wonder (AGP 8X)
fairly new 460W, less than 1yr old Antec trupower PSU
2x western dig raptor 10K 36GB RAID 0
10 fans total incl. HSF, chipset, VPU and surprisingly quiet.
1x DVD ROM. 1X DVD RW

Entire system is less than 1 yr old and nothing is overclocked or has ever
been.