troubleshooting white screen

Whenever I try to add graphics to my video from the graphics tab, all of my footage turns to a white screen. I work in ministry and produce videos of worships etc., and like to put image captions in the video, so this has been very frustrating to work with. Especially since you can not undo it, so I have just been starting over. It will sometimes work but not often. A lot of hours have been wasted editing a video for this to happen towards the end. Any help would be appreciated!