How do I re-install Imovie

My new Imovie is acting very strange. It doesn't let me move events to an external hd and worse, the content library (transitions, titles etc) has disappeared.

Do I just delete it from my app folder or do I get rid of fhe library in the movies folder? Will I lose everything I imported already??

Also, can I use USB2 to export to a external HD or do I need only firewire?