Help! graphics card problem

[m0ssman89]

Hi this is my first post on the forums and I was just wondering could anyone help me with a problem, I got my graphics card today and I just cant get it to work, ive installed it in the pci slot, its plugged into the power supply, I disabled the onboard graphics and ive even set the graphics to boot from the pci in the bios. Its showing up a blank screen and there's no POST beep every time I boot up. When i take the card out and enable the onboard graphics again everything works fine. can someone please help?

Specs
OS: Windows 7
Motherboard: Gigabyte z77x UD3H
Processor: intel i5 3570k
Graphics Card: HIS HD 7950 IceQ X2 Boost 3GB
Thanks

 

[Phage]

Are BOTH PCIE power cables plugged in ? I think your card takes two.
What PSU are you using ?