About 2 months ago I uploaded Firefox downloada bunch of songs onto my sansa fuze, everything was working fine. Then, about a month later, all the songs disappeared when I looked at Windows Explorer when the Fuze was plugged in. However, you can see and hear the songs on the Fuze. Also, some of the songs altogether disappeared. When I added new songs, you can see them in both locations. What are my problems here and how can I fix them?