Tivos displaying artist/song/album but not playing songs?

Hi guys, new to the forums but a long time Tivo'er...

My two new-ish (less than two years) Tivo boxes (both Series2, one Tivo and one Humax) will not play MP3 files anymore. My modest MP3 collection is hosted on my Windows machine in the basement, and I can view the folders published via Tivo Desktop 2.3a, but as soon as I choose to play a song, the artist/song/album info appears but the file doesn't start playing.

Also, when I use the Left Arrow to back out of the application, the box gets VERY sluggish, to the point that a hard reset is usually required to snap them out of it.

Any ideas?