Have you tried multiple slots in the computer? Sometimes if you are experiencing a conflict, switching slots will help.
If not, there are two possibilities:
1. the card is defective
2. the card is not compatible with your system
If you can, try installing the card in a different computer. If it works in that computer, the card is not defective and it is not compatible with your system. You will want to try a different brand or model card at this point.
If you try it in another computer and it doesn't work, the card is most likely defective and just needs to be replaced. Once you get it replaced, it shouldn't have any problems.