Add GPU & Pc will not power on - not a PSU issue

[Drawfirst]

New Build
I5 2500k
Gigabyte Z68xp-UD3P
2 x 4GB Corsair Vengeance LP CML8GX3M2A1600C9
BeQuiet silentwings CPU heatsink

Old Parts being added
ATi 5850 GPU
Seasonic 900w SS-900HP

I've been through that excellent sticky, but no joy yet.

With a breadboarded MB/CPU and ram, the PSU powers up no problem. Cant get the CPU's on-board HD3000 to output anything however. If I add my 5850 the PSU powers on for a second and switches off immediately and wont restart unless I turn off at wall and PSU switch for a few seconds. Ive also tried an older 8800gt and same result. I've also swapped back to the stock cpu cooler just incase I messed up the BeQuiet install.

It seems like a simple PSU power problem or a faulty GPU, but both components work fine with the Q6600 + Asus Maximus formula + 4gb ram that im now replacing. I thought it was the case switch at first but I've ruled that out now.

Any ideas before I RMA the MB?

 

[Outlander_04]

how are you starting it?

 

[Drawfirst]

I'm plugging the case switch onto the mb. Works 100% with just CPU & ram on the board, but as I've mentioned I don't know if it's posting as the hdmi port doesn't appear to be outputting

 

[Outlander_04]

try using a screw driver briefly across the contacts for the front panel switch to turn it on . This eliminates the possibility of a faulty switch .

Also try connecting to your monitor via a DVI connector