Which application were you using before to do the arrangement & burning? Sounds like there's been xtra applications installed & the priority app has changed many times. You could I guess select an mp3 file, go to File>Properties>Open with... & choose your app & select always open with. But I presume that you were using WMP before right? If yes then make that the default app to open your mp3's. OR whichever app it was. You might need to open them all up to see which one it was.