I've been searching for a solution to my problem but I've only founf others with simliar problems - no solution. This guy describes his problem exactly like mine:
"i have a stange problem, a couple minutes after startup my taskbar will
revert to the windows classic style (from the xp style) and the windows audio
service will stop. i then get a "no mixer available
error message if i try to open volume control. in services.msc the
windows audio service is set to auto, as is the other services it is
dependent on (plug and play and rpc)."
I will also add that the styles will sometimes switch back and forth between XP and classic style. I can fix both problems by enabling styles in the performance menu and starting Windows audio in the services window, but I have to do this each time I start up. I think the windows audio service is crashing and messing everything else up. Can someone help me figure out how to get everything running smoothly again?