Computer will not power on with PCI cables plugged in

[Ham117]

Motherboard: ASUS AM3+ CROSSHAIR V FORMULA
Power supply: Corsair Builder Series CXM 750W Modular 80 PLUS Bronze Certified ATX/EPS PSU
Old power supply: OCZ Technology ZS Series 750W 80+ Bronze Power Supply

I rebuilt my PC when I bought a new case about a month ago and when trying to run it the fans would twitch and the PC would not start. I bought a cheap graphics card (Nvidia Geforce GT 610) with no PCI cables needed and the computer ran fine so I opened an RMA and sent my R6970 back. About a month later I received a replacement R7950 (Very kind of them).

I fitted the new graphics card after taking the GT 610 out and the computer ran fine for about 30 minutes. It powered off without reason and would not turn back on. The fans would twitch but it would not start. If I unplugged the PCI cables the computer would start and the GPU would run its fans at 100%. If I removed the graphics card from the computer but left the PCI cables plugged into it the computer would again not start. I bought a new powers supply and tried again but the computer will not start if the PCI cables are plugged in.

Any ideas on what is causing this?

 

[blazorthon]

Assuming that there isn't a short somewhere, that PSU may be faulty. It's also possible that you got a faulty graphics card (I've hear of someone getting three faulty cards in a row before).

 

[Ham117]

Assuming that there isn't a short somewhere, that PSU may be faulty. It's also possible that you got a faulty graphics card (I've hear of someone getting three faulty cards in a row before).

I have replaced the power supply and the graphics card worked for a short time so i don't think the card was faulty when I received it.