Did you do a reinstal or something? if so a quick google search gav eme this
"If you have Windows xp and service pack 3 and are experiencing difficulties with having no sound after a fresh installation,try this,it works
1) Open Regedit and go to :
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Windows\CDSVersion
2) Double-click CDSVersion and change it to 200, then restart your system.
100 (hex) means its sp1
200 (hex) means its sp2
300 (hex) means its sp3
3) Install kb888111xp2.exe (Microsoft UAA Patch which should be available from your Audio driver folder)
4) Install audio driver
5) Change CSDVersion back to 300 (remember this or else you system will think it's still SP2 and many SP2 updates may reemerge in your Windows Update
6) Restart your system"
