Are you using LW's player?
Have you tried using different players?
Does the same thing happen?
Are the different songs that play ones that you've downloaded before, or are they completely random?

If the same thing happens with multiple players, maybe you should update your AV & scan for viruses.
Have a look through this thread for more info about security programs: http://www.gnutellaforums.com/330543-post11.html