Hi this is urgent so please help thanks

It has been a while since I had used movie maker but it worked perfectly while editing the movie.  It is an approximately 20 minute movie that I want to upload to youtube. However when I save the movie (it takes about 40 minutes to do so) it is saved and all is good until I try to play it. It only displays a black screen throughout the entire movie with only the audio playing.  I tried a lor of didn't settings to save it like for computers or phone or 1080p displays but it always turns out to be the same black screen with audio in the format of a video. How do I fix this?