Just go to /YourHardDrive/Users/YourUserName/Library/Preferences/ and delete the files com.apple.iMovie.plist and com.apple.iMovie7.plist then relaunch the program. Deleting a program's Preference file will reset that program.
I am having the same problem since I updated it to v7.1.2.
The only difference is that I receive a message saying that has to update thumbnails of iPhoto videos. I can ask to that now or later. If I chose now, it quits unexpectedly. If I chose later it freezes while updating thumbsnails.
I deleted the files you suggested but problem continues