songs won’t play in WIndows Live Movie Maker

I have created a movie with video and photos, done all of the transitions etc (10 hours worth of time!) and then added songs.  None of the songs will play.  They are mp3 files.  The volume is up all the way for the songs.  It will play sound from the videos in between songs.  Just to test it, I made a new windows live movie maker project, added some of the videos and photos and the same songs as my original project, and the songs play! I have tried to take off a song and re-add it to the original project and it still won't play.  I didn't do any of the transitions for the new test project.  Is there some sort of control - other than the music volume button - that would affect the song sound I may have inadvertently hit? I have re-booted my computer.  I appreciate any help.  I don't think it is a problem with the program since it will work fine when I start a new project, and it always has worked in the past.  There is just something I must have done to mute the songs, NOT the video sound, on my project.  Thanks!