First thing I would recommend is go to
1. Http://windowsupdates.microsoft.com
Run all the updates and see if there is an updated driver for your sound card.
If that doesn't help, go to:
START | Settings | Control Panel
Switch to Classic View if it's not already selected,
Double Click on "System"
Go to the "Hardware" Tab
Click on "Device Manager"
Look for any items with an exclamation point.
Remove the items with an exclamation point and reboot your computer.
When your computer reboots it should automatically install the best drivers for your system.
If it doesn't you may have to find the drivers associated with device that's not functioning.
Hope this helps.