Sorry for the late reply. I really am not familiar with this phone (yet), so I'll just throw a couple of generic things at you.
Have you checked that your music folder on your sdcard doesn't have a ".nomedia" file in it?
Have you tried a different music player?
Try going here: settings -> apps -> all -> Play Music
Then select clear cache. If that doesn't do it, go back and clear both data and cache.
good luck