GTX 285 running terribly PLEASE HELP!!

OK

Here are the specs

Antec 900 2
Zalman Heatpipe Cooled 750 Watt PS
Intel Core i7 920
GIGABYTE GV-N285-UD-2GI GTX 285 2gb
6gb ddr3 ram
EVGA x58 SLI LE e757
Windows 7 unregistered

Now here is there problem, I have just upgraded from an 8800GT, thinking that my poor performance in applications such as 3dMark and games was due to the card being out dated. To the best of my knowledge the 8800GT was not running properly and I thought that it was probably a hardware defect on the card, so I proceeded to shell out 400$ for my GTX 285. There has been little to no improvement.

Ok so yes I have installed the latest drivers, and checked that there all the right power cords are plugged in. It is definately in a PcIe x16 slot and I have tested it in a pcie 4x4 slot and a 8x2 slot with worse results. I have installed CPU-z and got nothing out of it and really I have absolutley no idea why my card is running so badly.

I thank you for all advice and help, but I have limited computer knowledge so if the advice is something like - I dunno but really if you could if expand a little on what you are suggesting that would be fantastic!

Appreciate all contributions and hope to get this sorted so I can play Modwfare2 like everyone else

Windows 7 unregistered?

update the drivers maybe?