Also, since voiceover is not working it might simply be a corrupt preference causing that. Try deleting preferences. To delete preferences, open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new library. Reopen your old library to get back to your projects. Deleting preferences is a safe
procedure that will not cause data loss or disruption to your project.
To rule out that the issue might be confined to just this one project, create a new project and see if the voiceover feature works there.
-- Rich