This was a puzzler and happened to me at home! When I would boot up Windows Media Center, I no longer was getting any sound in the program (sound in Windows was working fine however). No sound in live TV or recorded TV. However, if I opened up a regular video in the Video Library from within WMC, I would get sound! Very odd. Tried a System Restore, but it kept telling me it couldn’t restore files from the C: drive. I re-setup the speakers in WMC and re-setup the tuner and still: no sound. I then removed the sound driver and TV tuner driver and let Windows re-detect them and viola: sound was working again!
I love Windows (not).
– Soli Deo Gloria