iPhoto not playing videos

Some of my videos in iPhoto won't open or can't be transferred to Facebook. What's wrong? I'm all updated to Mavericks, which may be the issue. A few days ago I tried to open my videos in iMovie and they worked. Now they don't appear in iMovie at all, even when I try to make a new event. I can currently play all but one video in iPhoto but can't move any of them to Facebook or iMovie.