Great App But Help!!!

Ive been using iMovie for ages now, and I think it is an amazing app. But for some reason, my movies wont play even if I erase its memory. I was in the middle of creating a movie when it showed only black where the video was supposed to be and whenever I pressed play it showed as if it were playing but without audio nor music. Does anyone know why?

TrueTricksYT about iMovie, v2.2.3