This isn't my first time using iMovie, so I don't know what's wrong. I haven't had this problem before and I've been using it for 3 years. I'm making a video for science and I take youtube clips, transfer then through keepvid.com, and put them into my video. But at one point when I did that everything went haywire. It doesn't show the images; pictures and video. It doesn't play sound anymore, and all of the clips I got from youtube have a yellow yield sign with '!' on it. This is also effecting everything I created. When I go to a past movie it wont show the words, or the pictures. Is there a way to fix this??