My sound on Windows movie maker won't work?

yes, windows movie maker support mp3 and wma format well, so I think there is something wrong with your converted files, you can try to choice a better converter to convert the downloaded youtube videos to right wma or mp3 sound files for Windows Movie Maker, I used RZ Audio Converter, it can convert any audio files or video files to any format audio files, such as convert downloaded youtube videos to right wma or mp3 files for windows movie maker, etc, easy to use, you can yahoo or google search and download RZ Audio Converter, hope it can help you.