Booting Issue

Hello all.

I've had this rig for about a solid year. About a month ago I pulled it apart and installed all my hardware into a different case.
From then, I have been experiencing this problem with both of my old and new cases.
This is what happens:

*I turn the computer on via the power switch.

*Everything turns on for about 5 seconds, then shuts down.

*Remains off for about 3 seconds, then turns itself back on for another 5 seconds.

It completes this cycle repetitively until I isolate the power from the computer.

After trying to boot the computer a couple of times, it goes into windows and works fine. I only experience trouble trying to turn it on.

I have a suspicion that it's something to do with the pins where you connect the power switch/HDD Led's on the motherboard or something to do with the power supply.

My hardware is:
MSI P55 GD65
i5 750
XFX GTS 250
Samsung 300 gb.
G Skill Ripjaws 4gb (1300)
Coolermaster real power pro 550w.
Thermaltake Xaser VI MX.

Any ideas where I should start to look at?

Thanks, Shappo.