Great but one problem

So when I am making a song or horror movie, sometimes when I press play, the clip does not roll, then when I play it on screen its just black and it does not show the video, its very frustrating when you worked on something hard for hours then it just does this and you have to do it all over again, you cant upload it either if its doing this im very mad, if you dont fix this I will be extremely angry

Hssjjsjskskksksk about iMovie, v2.2.3