They may very well be bad files. See
Recognising Fake files. Then for tips on searching see
How to find music
If your using the limewire player, try playing them in a different player. The limewire player is not very good and is prone to skipping, and cutting out, especially while using your cpu for other things. In LW go to Tools>Options>Player, untick the box and click apply. Then songs will launch in your default player.
See this thread for related info:
CODECs list and alternate players for Movies.