Editing a MP4 file That Has Already Been Made in Movie Maker

So, I had edited a video in movie maker and put my voice over some footage and saved it. I added the voice, by inserting "music." Then, I saved the "movie," so that I could open the MP4 file I just made, and add accrual background music. But, when I opened the file, no sound was playing, is this because I already edited the file in movie maker? If I saved the MP4 file that was already edited a second time in movie maker, would there be sound?