[brusselsshrek]

I had this same problem on Windows XP Professional suddenly occur - speakers stopped working, RealPlayer giving the message, "Cannot open the audio device. Another application may be using it", iTunes player simply not playing.

Went to "Component Services" as suggested and found "Windows Audio" (after looking for "Audio") which was stopped. Clicked "start the service" and everything worked fine.

Thanks for posting the solution! I would never have found it otherwise.

Hope this post helps somebody else.