c150- does not show music files on device

When I connect my Sansa c100 (c150- 2GB) to my computer and open Windows Media Player, WMP says “There are no files on this device”… yet it is over 3/4 full.  I wanted to delete some music and add a different set but cannot delete because the music files do not show up.  Any suggestions??

Thanks so much.

If anyone has this problem, try going to “Sync” and clicking “Refresh devices”