created an account to help you out a bit.
I receive the problem also, where the audio after I random period of time just 'craps' out. When opening the volume mixer, the audio device that I'm using is still there, along with all the applications, however none of them show as playing any sound. Opening task manager, and restarting the service 'Audiosrv' fixes the problem, however I have to reopen all programs that are making sound. Note that this only happens after a fairly long period of time as I'm one of those people that never restart their PC, it happens after about one - two days of being on.
I hope some of this info helps!