P5K-E Power Problems

[latency]

Got a custom rig in for repair with a strange motherboard issue-

It's an Asus P5K-E board, with a Core 2 Duo, 4GB of OCZ Reaper X, and a Radeon HD3850.

Basically, you switch it on, the fans spin up, and then a few seconds later, it switches off. Then, a few seconds later, it comes on again, and does the same thing.

It continues switching on and off until you kill the PSU.

Tried:
Reset BIOS
Different PSU
Different Graphics card
Don't have any spare DDR2, but same problem occurs with RAM removed
Removed motherboard from case and running open on a desk- no shorts to case
All other cables / components disconnected
No beep codes from system speaker

Looks like the Mobo is dead to me, but I don't have a spare CPU to eliminate that from the equation.

Any thoughts?
Ta all!

[saltynay]

Doubt this will work, try turning off the psu leaving for 5 minutes then turning back on and immediately powering up the pc. This causes a small surge of power which works for my computer whenever it won't boot randomly

[latency]

No dice.

Something new though- removed the CPU and started it up, no output obviously, but it didn't switch itself off again.
Can a mobo initialise without a CPU?

Edit- just asked google that question, and found a forum thread describing the same problem without another motherboard, poster there found it was a faulty mobo.

Will go with that unless anyone else here says otherwise!

[Westy5]

Seems the logical answer, given your trials