windows media player encountered a problem while playing the file

Hi, I just bought my laptop.. and everything was ok. I could listen to all my music in my library, but today I wanted to do the same thing and I couldnt anymore! There was a message that said: "windows media player encountered a problem while playing the file" ... I dont understand what happened to my WMP! Somebody conected wireless yesterday and my laptop asked me if I wanted to share with that computer my files.. I press "no" and maybe thats why, because I cant find any other reason why this happened to me! Please help me!

VICTORIA