I have the Razr M and have had it for about 6 months now and all of the sudden it deleted all my music out of no where. I uploaded more music and then it deleted that too. It doesn't, however delete any of my pictures of videos or anything else just my music. My Play Music app seems to be not working at all because i sent a song through text message to my number and it comes out terrible quality for some reason almost like i recorded it with my phone, but on my computer the file sounds fine.
A couple of suggestions:
1. In Settings/Apps try clearing cache for the music player
2. Does it sound any better with headphones?
3. If you do a file search can you see the music files?
4. Try downloading another music player from the play store to see if that fixes it.