I think Selden has a good lead for you there. I recently found myself in the same situation, only it was with Zoom Player, and only MP3 and AAC audio failed to play... other formats were fine. Somebody at the ZP forum finally suggested I check to see if I had reinstalled the MB's audio drivers. Sure enough, I hadn't, but as soon as they were installed everything played again.
Also, since you're missing all audio output, check to see that Windows or VLC's audio isn't muted in the Windows audio mixer settings. They're known to sometimes mute themselves for no apparent reason.