Yes, it never hurts to delete preferences. So try that procedure again.
Also, try resetting the system management controller as I mentioned in an earlier post.
You have a conflict somewhere on your Mac. Here are a couple of other things to try:
Try opening iMovie in a new user account, either one you create or by using the Guest account on your Mac. See if iMovie works properly there.
Try doing a First Aid scan from the Disk Utility app on your Mac.
All else failing, try redownloading iMovie from the online app store. To do that, move your current iMovie app from the Applications folder to the trash, but do not empty the trash. Then go to the app store, sign in, and navigate to
your Purchases folder and redownload iMovie. If for some reason you can't get a new download, move your old iMovie app from the trash to the Applications folder.
Hopefully you can isolate the conflict with one of the above.
If nothing works, then you might consider calling Apple Support and talking to one of the savvy techs there. They have the capability of remotely accessing your computer. Click on the Contact Support item in the upper right hand corner of this screen. Navigate to a place where you can input your telephone number.
Good luck with this.
-- Rich