What's the problem? (pc pwrs on, pwrs off in a few seconds)

[BYTEr]

So currently I have the bare minimum of my pc sitting on my desk.

Problem:
-Connect the PWR on pins.
-PC powers up for 7-8 seconds and then powers off.
-Pause for 2-3 seconds, then powers on again for 2-3 seconds and then off again.
-Phase LEDs show green,green,yellow,red.

Setup:
Gigabyte EP 43-DS3R
E6600
OCZ 850w PSU (also have an generic 550W)
2GB G.Skill 6400
Titan Fenrir TTC-NK85TZ CPU Cooler

ATX 12V and the main ATX plugged in.
CPU and CPU cooler on (cleaned and re-applied with new TIM)
1 stick of RAM in.

What I've tried so far (no success though ):
-OCZ PSU
-Generic known working PSU
-Both sticks of RAM individually, no RAM, 2 sticks of RAM togerth.
-Clearing CMOS

All lead to the same problem as I mentioned above.
So what is wrong, what can I try? Who or what is at fault?

Thanks.

 

[J.B]

Have you got the PSU and GFX power connectors attached?

One thing I would try is building it outside the case as something may be touching and shorting out. Also this if a good way of reseating and checking you connections.

Could try disconnection the power switch and then shorting the pins out with a small screw driver. Could be a dodgy button, bit of a long shot but you never know.

Failing that the motherboard is probably faulty.

 

[BYTEr]

Have you got the PSU and GFX power connectors attached?

No GFX card. All other PSU connections thats are needed are in.

One thing I would try is building it outside the case as something may be touching and shorting out. Also this if a good way of reseating and checking you connections.

It is, literally mobo sitting here on a ESD sheet.

Could try disconnection the power switch and then shorting the pins out with a small screw driver. Could be a dodgy button, bit of a long shot but you never know.

Yep what I'm doing.

Failing that the motherboard is probably faulty.

Well the gigabyte motherboard I bought to replace a possible faulty motherboard, still could be faulty though.

CPU/CPU cooler dead? Possibly?

 

[RJC]

What GPU are you using, and have you installed the 4 or 8 pin for cpu power.

Edit: When you say no gpu do mean no gpu or no to separate power for the the GPU.

 

[BYTEr]

What GPU are you using, and have you installed the 4 or 8 pin for cpu power.

Edit: When you say no gpu do mean no gpu or no to separate power for the the GPU.

I have a 8800 GTS but it doesn't change anything so I left it out.

I'm using all 24pins and the 12V ATX.