try to make sher that your music and videos are on the main hardrive(if windows) go to my music then right click on any one of the songs that are not working. Go to properties at the bottem, click and see were it is located. If doesn't work make sertain that all music file tipes are checked in Zune under settings.
For some reason Zune isn't synching my music and videos anymore even though they're in the right file, also it won't change my music from my device to my collection, any suggestions?