PC sees power for 5 seconds, then reboots

Hey guys,

I've run into a problem that i have never encountered with a computer before and am really lookin for some help if someone can ablige.

I've moved residence recently, transporting the comp with. I set it up and fired her up about 2 weeks ago, no issues :) however, i needed to re-arrange my room so packed her up and moved her around. Anyways 2 days ago i plumbed it all up again, but this time the problem started.

This is the what happens in sequence,

I plugged the power into the wall (always the last thing i do) once all the cords were ready to go.
Flick the wall power on and then the power supply power switch on the unit.
I press the power button on the front face and get the LED to fire up showing power.
All the fans fire, the DVD shows a response and i can hear the HDD i believe. This happens for about 3-5 seconds.
Then it begins to power down, like its turning off.
2 seconds later i repeats the power on and off issue.

I don't get power or signal to any I/O devices. Keyboard, mouse, monitor.. nothing.

I'm not 100% on my specs, but i believe these are correct

MB: Gigabyte S-series
Chip: Intel Duo-core 1.8
RAM + PCI: 2 Gig + 256MB Gigabyte 7600GT

Thanks in advance to any help anyone can provide :)

Cheers