If there are any legacy devices sitting around, disable them and try again.
Another thing to try is go into safe mode, go into control panel, and remove all the drivers. Then reboot in normal mode and get XP to detect and set it up again.
Just to troubleshoot further, try different speakers, and make sure the volume is turned up. ~Apex1x
Miller's Law:
You can't tell how deep a puddle is until you step into it.