Computer Will Not Power On (sometimes)

[lestercat]

I have a fairly new system, spec's below

2.66 Quad Core
MSI P6N SLI (latest bios)
8 GB Ram
PNY 270 GTX Video
650w corsair power supply

The problem I have is sometimes when the computer starts it wont boot unless while it's on I unplug the pci-e lead from the power supply and plug it back in. This lead has the 2 6 pin connectors to the video card. My question is would this be a problem with the power supply or possibly the mobo. I have tried different video cards and get the same result.

 

[r_manic]

Check power supply and mobo. Also, try resetting mobo.

 

[jsc]

What happens, if before you boot, you momentarily turn off the switch on the back of the PSU?

 

[lestercat]

No difference. I'll just live with the side panel off until I get a new PS.