Hi. You don't mention your O.S. If it's 9 you may have a corrupt file name or it may have been shortened and they need to be reconfigured. If you run iTunes, simply open up iTunes, highlight the mp3 files, and then go to add to library or open in iTunes script and they should go back into the iTunes player and open whenever you start up iTunes. I don't have OS X so I'm not sure but I believe the same procedure exists within iTunes to add to it's library and use it as your player of choice.