|Checking updates for latest drivers is a good way and also :|
(Assuming that your video card is not broken working)
Check your BIOS for settings of O/B to PCI-e. It can be in Advanced>Chipset>SouthBridge.
Check your BIOS for latest update and also Video Card's Bios.
(Theese bios updates can be a little dangerous if you never did before)
Finally, one week ago I bought a Graphic Card (HD4670) and spent my 12 hours to set it to work. Bios could't set auto swich to PCI-e. I have to do. But nothing happened. Then I give up. Started to think maybe my board or PCI-e slot crashed. Gave it back and bought an other card HD5570 and pluged it. It set to Bios and removed the O/B GP. I did nothing. It worked well.
So, acording to me if you have a chance to try it in another computer, first do it. If it works good, you can try to find solutions.