What happens if you navigate to the music file in a file explorer and click on it? Does it then give you an option to play? If not, you may have a conflict with the decoder/player and the files. Where did the files come from? Were they ripped from a cd with a specific program, or were they downloaded from somewhere?
Make sure there are no funny characters in the file names too.
Lastly, I would try a different player. Google Play Music
, or Poweramp