Motorola V400

On my v400, i'm having a problem with my music section. You know you download some songs, assign them to category so they are easy to find, cool. It looks nice for a while, but then my v400 doesn't show the files anymore. You understand? they are still there when i want to change my Loud Detail or make an alarm, but I can not access them if I wanted to delete them. This is crucial, cause I got mp3s on my phone which are taking up a lot of my space and I cant get rid of them no more. If anyone experiencing this too or know how to solve it, please let me know.

Thank you