move music files in iTunes Library won't play in Music.app

I have had iTunes for years before the Music.app came along. I imported a lot of cd's into iTunes. Currently in Music.app the media files are reported to be in /Macintosh HD/Users/jameslit/Documents/iTunes/iTunes Music. Music.app will not play most of the files. The files will play if double clicked directly (not in Music.app). How can I fix this? All suggestions appreciated.