You could do a test to establish if your Sound Card is working correctly. Accordingly, I have copied and pasted a very simple test from Ehow, which you could try.:-
Checking a Sound Card with the Device Manager
Click "Start," then click "Control Panel."
Double click on "Device Manager."
Locate "Sound, Video and Game Controllers" in the list of devices, and click the plus sign to expand the list.
Right-click on the audio device listed and select "Properties." The various property tabs will have information about the sound card, its driver and whether it is working properly.
Hans.