I already downloaded the newest driver for that card but it still doesn't work :S
Man...the AMD cards are a PITA! I've had so much trouble with mine when updating firmware and installing.
I don't know for certain, but I'm guessing you're going to need to uninstall the Catalyst (which isn't easy at all) and then reinstall.
The things are finicky and if you do something out of order, you will never get it working correctly.
Did you install the drivers before inserting the card? If so, I think you'll have to do an uninstall/re-install. The driver must be installed first (if I remember correctly)
There's tons of info around the interwebs that offer guidance in uninstalling. You may want to Google a few searches on proper installation of the card.
What ever you do...do not attempt to uninstall the Catalyst without following a good step-by-step guide! I did that once and it ended in a complete reformat of my HDD.
Sorry I can't offer more. Perhaps someone will give you some better info before you begin uninstall/reinstall....it really is a time consuming pain!