Can't Delete 5 Audio Books from Internal 8 GB Memory...books do NOT show on PC Explorer

I had somethiing like that happen once. I found that a music album on the external disk had an .m3u playlist included with it (everything else I keep on a Fuze has a playlist in the Playlist directory, or is a special music Singles directory so I can set it to shuffle. It would show up in my Playlist list and would actually play if I clicked on the playlist, but the folder was invisible on the PC until I did some computer hacking to read the hidden folder. It would still not delete.  I finally saved off everything I wanted to keep onto a PC, formatted the Fuze & the external disk from scratch, and reloaded everything. Haven’t seen the darn album since.