This isn't meant as an insult or anything, I'm just not familiar with your level of technical knowledge: You have checked device manager to see if you're missing any drivers, right? If not, you can go to start -> right click My computer -> Manage then to device manager. In there, you can see if any drivers are having problems/not installed. Secondly, you can download and run unknown devices. When run, this program identifies the specifics of any hardware which is missing drivers.

Those are my first thoughts. Anytime I've installed a sound card, it just works for me unless the card is dead. Let us know if this helps or if you're still having some issues.