As Ian says, deleting preferences does not delete projects or cause loss of data. When you delete preferences iMovie opens in a new blank library. No projects in it. You need to return to your original library to access your projects. Close iMovie and go to your Movies folder (Go/Home/Movies) and double click on the library icon that contains your projects. iMovie will open in that library and you are good to go. If your original library is not in your Movie folder, but on an external drive, then navigate to the external drive and open the library from there.
Another way is to open iMovie and click on File/Open Library/Other and navigate to your old library.
Finally, to cover the bases, open the Projects browser and make sure that the proper library is selected at the top of the screen.
As for the "sharing failed" issue, that can occur for a number of reasons like insufficient application space or destination space, corruption in the project, a corrupt preference, etc. Check to make sure that you have sufficient free disk space. If all O.K. there, try the delete preferences procedure again and see if that cures it. You can also create a new project and see if you can share from there. Otherwise, you can expand your project timeline out full length with the slider located to the right and above the timeline. Then scroll slowly through the timeline, looking for black frames, white flashes, artifacts and any other signs of corruption. Cut out any that you find and try to share out again.
Also, take a look at this thread and see if the solution there works for you. The poster there moved the project to a new library where the "sharing failed" issue did not occur. In other words, try a new library. Here's the link to the thread.
https://discussions.apple.com/thread/7073179
All else failing, you might try contacting Apple Support. The techs there have the capability of remotely accessing your computer that we cannot do here. To contact apple support click on the Contact Support item in the upper right hand corner of this forum’s screen. Navigate to a place where you can enter your phone number.
-- Rich
