Hiya,
I lost my sounds in vista x86, Literally without a reboot etc... Weird
Uninstalled card from system/device manager and rebooted and then redid drivers while windose was also doing the same
All sorted
Dunno what OS/Card you got but should fix problem as sound was ok previously
Have Fun
Ciao
Def
ps: Check codecs if above fails and re-install if necessary