Need help diagnosing the cause of this problem:

[SerenadeRB]

Preface:
My system was running stable for awhile, and while playing the Sims 3 just shut off. After turning it back on I used default BIOS settings to try and figure out what happened. After loading the OS it took about 3 minutes and it shut off again. After a few more tries it got to the point where the power would "flicker" (See video below).

Question:
Could you guys help me figure out what the cause of this issue is? And how I should go about fixing it.

Extra Info:
I tried turning it on with a different cpu (E8600), then tried without RAM, without a HDD, and no Video Card and nothing changed.

Video:
http://www.youtube.com/watch?v=yJ9ssWhEBDI
Note- Video was taken after computer was "turned on", each time the lights come on it starts up and shuts off.

Specs (if they help):
Asus Rampage Extreme
Intel E8500
Mushkin 996601 RAM
WD Raptor X
Watercooled

[Oberon]

I would have guessed a heat problem originally, but that's probably not it if you're still having the same problem after swapping the CPU.

I'm personally leaning towards a power supply issue. You wouldn't happen to have a power supply tester or an extra PSU around, would you?

[little_scrapper]

loose cables

[5ILVgearX]

most likely PSU, check your rail ratings on your bios.

and hows that northbridge temp?

[3Z3VH]

Try unplugging any not-necessary-to-boot components and booting the machine.

I second the fact that the PSU seems to be shot. Lemme guess, an Antec PSU ?