Hello there! If after deleting the plist file you still have issues with the iMovie then imovie.app is corrupt and will need to be reinstalled. Your mac should of came with 2 gray disks. One disk will say osx the other will say applications. Use the applications DVD to reinstall iMovie. Without the disks we will not be able to reinstall iMovie. If you cannot find the disks then we will either have to buy a newer version or use a friend/family members application disks ( this works about 50% of the time ).
If you go to iMovie / Preferences / General check the box Show Advanced tools, also you should remove all of these then restart before doing that:
In Macintosh HD / Library/Preferences:
All the files with
iLife.plist in the name
In your user Library:
Please accept the remote tech support if you want me to try to reinstall your iMovie application for you thanks.