Vista - No audio for media playback

I have a machine with an integrated realtek audio card. When I boot Vista or
shut it down, I hear the music the system plays. I also can hear other
system sounds. The hardware device manager says my drivers are installed and
working. However, just this week the system stopped playing audio when
trying to listen to MP3s, mpegs, etc.... When trying to use media player I
get a message "Windows Media Player cannot access the file. The file might be
in use, you might not have access to the computer where the file is stored,
or your proxy settings might not be correct." but the skin looks like it is
playing. I can't play the files with itunes or any other audio software I
have. ANY SUGGESTIONS?