Help with installing an Radeon HD 6950

I've spent awhile trying to assemble this myself but I can't seem to find anything else to try. I apologize for links but I figure its the easiest way to show all of my computers parts.

This is my current computer http://www.newegg.com/Product/Product.aspx?Item=N82E168..., with the only modification being this http://www.newegg.com/Product/Product.aspx?Item=N82E168... replacing the fan it came with.

I ordered a Radeon HD 6950 to replace my ATI Radeon HD 5450. I was able to remove the 5450 from my PC and replace it with the 6950. After installing the drivers on a CD that came with the 6950 I tested it out by trying to play a few games on Steam. They were incredibly laggy and much worse than my original card.

When I look under Device Manager-Display Adaptors it shows "ATI Radeon 3000 Graphics." When I removed the 6950 and put back in the 5450 it correctly named the card.

If anyone could please help me get my 6950 to run, I would appreciate it. Thank you for any help.