Ok... This is a serious one because everyone is saying the same darn thing.
Control Panel, System, hardware tab, device manager. Find your sound device, Disable and re enable it. See if that works. If not. Un install it. Reboot computer. It should pop up saying you have new hardware and it is being automaticaly installed. You may have to put one of your driver disks in to find it. Afterwards it should be enable and "working properly". If not call tech support and tell their asses to fix it.