This could be a driver problem, so uninstall all drivers from your sound control hardware, restart the computer and let windows install them again in the order that windows requires.
Make sure you have the latest direct X software, (9c) use Windows Update to check and at the same time see if there are any Hardware Updates.
Go into Programs, Accessories, System Tools, System Information and on the Tools Menu, select Direct X Diagnostic tool and see if any problems show up there.
With the software you are running make sure you have at least a 2.5 GHz CPU and 1 GB of Ram.
Hope this helps.

Bill