Vista - Sigma Tel audio service stops on hibernate

No sound....My sigma Tel audio service stops on hibernate. When I go into service to restart get error message : service started and stopped. Some services required others to be started....etc. I can restart the audio service with a reboot. Can't figure out why I loose my sound........everythings leads back to service issue. Also had dell support reload audio drive. I have a dell xps 420 desktop, anyone having a similiar issue, any ideas??

Do you have the newest audio driver? Which Vista service pack? Dell XPS's are way overpriced and they don't even put in a sound card that Vista accepts.

dell support reinstalled audio driver, osp-vista premium 32bit, sp2, integreated sound, bought the machine and 22" monitor from a guy that went to a lap top $400 (like new with warranty till 2010) dell techs can't figure out sound issue they keep reinstalling audio driver?. Think your right about the sound card. What if I put a sound card in the machine replacing the integrated sound? Sound works untill the machine goes to sleep.....have to reboot to get sound back