c240-invisible music

I have had my c240 for a few years…i have a micro disc in it, which is full along with the internal memory. Recently, Windows Media Player has stopped recognizing most of the music on my player. It shows part of what is on the micro disc, and says that there are no files on the internal memory. However, it still says that there is no space to sync files. I can still access and listen to my music that is on the player, but since WMP does not recognize it, I cannot delete or add any files to the player.

any advice?