I suggest you take a look in two places:
a. Event Viewer
b. Device Manager.
How To Use Event Viewer - http://www.bleepingcomputer.com/forums/t/40108/how-to-use-event-viewer/
You are only interested in errors
, not information items. Look through the whole list, each tab. If you see an error that indicates it has anything to do with audio or sound...double-click on the line item and examine the detail.
Post the details for such in your next post.
Start/Run...type devmgmt.msc and hit Enter. That gets you to Device Manager. If you see any yellow or red markings by anything...post the detail for that item.