greysky1,
Try downloading a couple files from here and see if they play right:
http://www.magnetmix.com/audio2.shtml. If the files from that site play right, then I think it's a pretty safe bet that you have some bad files.
The fact that any of your files play correctly seems to suggest that the other files are corrupt. Also what type of files are they(mp3, wma, ect)?