i've just resolved the issue, I rebooted and the sound was there!
I've just made a movie in movie maker and then saved it as an mpeg mp4 and the sound was not there, so I saved it in wmv mp4 format the sound is not there. I checked the project file and there's no sound there now either. It's an hour long film for my nieces 21st birthday, I've spent about a week on putting it together and I'm now desperate to resolve it. Please can you help?