Open the case, take out the soundcard from the PCI Slot. Reinsert it. Make sure it is firmly planted into the PCI slot. If you are utilizing onboard sound (That means it is on the motherboard) then it is already properly installed on the motherboard.
Download Direct X. After it is installed, click start --> run --> Dxdiag.
Go over to sound/music. Test your card, see if it works.
Make sure you have the latest drivers, for everything sound related.