Windows 8 Movie Maker suddenly lost sound – how do I fix this?

Was working fine then lost sound. It's not the music files as they were all working previously and the same projects that worked before no longer have sound. I have uninstalled and reinstalled. I am making multiple small projects instead of a larger one. Converting to a movie works fine - the movie files have sound but I need to be able to hear it when working on a project. Is there a volume mute setting in MM that I don't know about? This is very frustrating because this has happened to me in years past using XP and Vista versions but I don't remember how those were resolved. I would think by now Microsoft would have solved this problem! Help!