Do you have a sound card installed or are you using the onboard sound ?
Check device manager for any yellow exclaimation marks against sounds and video controllers.
Start / Right Click My Computer / Select properties / Hardware / Device manager expand the +key under Sounds and video controllers. Find your sound card/onboard sound and right click and uninstall.If XP it will load the generic drivers on reboot.
Though if you have the motherboard drivers on disk,use these first.
Just to verify,if using a sound card...make sure the onboard sound is disabled in the bios.