Q: weder meine Bilder noch meine Musik werden bei i movie angezeigt, wenn ich auf das Symbol klicke

Schau mal hier, Nicole

"When you select photos in the Photos pane of iMovie, one or more photos or albums appear to be missing."

OS X: If you can't see iPhoto images in other apps - Apple Support

There are several suggestions given in that thread. Be sure you have a good backup first.