Why can't i see my iPhoto pictures in iMovie?

I have been using i movie for so long, and this has never happened before. When i put pictures (from iphoto) on my imovie project, they dont show, like i CAN put them, but when i play my movie, you cant see anything, its just plain black. I dont know what to do, and i need them to work A.S.A.P! I have reseted my computer, imovie, and tried with different pictures. Please help!