Help please - Problems Installing PCIE Graphics in Dimension E520

I have just installed the POV 7600GT in the E520, Changed the bios setting from auto to use pep when installed. Rebooted and for about 30 seconds the screen displays as normal then begins display lines and distorts the picture before going blank. The screen then displays digital input message but no picture. Is there any part of the setup that i have messed up or would it look like the card is faulty. I was using the onboard graphics prior to this so is there anything i should have done to uninstall this prior to adding the new card?

 

Any advice or help would be greatly recieved.

 

Thanks