I have been following this thread because I have the same problem as Ally T. My MacBook Pro is a late 2011 model (2.4 GHz, Intel I7 Processor w/4 GB of Memory) On 3/31/2016, I upgraded the OS from its original OS X Lion version to the new El Capitan OS (Ver. 10.11.4). Very soon after the upgrade, I began experiencing a number of problems with the iMovie application, including the most recent - missing iMovie project files. After launching iMovie, then clicking on the "Projects" button, all I get is a black screen with 2 icons in the center of the screen (create new movie / create new trailer). I have followed Jim W's advice to Ally T and deleted the "CurrentVersion.flexolibrary" file from my movies folder (and yes, all of my missing project files were/are also in that same folder). I then restarted my Mac, and launched iMovie. When I clicked on the "Projects" button, the same black screen appeared with the same "New Movie / New Trailer" icons in the center of the screen, but no Project files are shown / listed. I am seriously contemplating uninstalling iMovie and then attempting to re-install it from my external Time Machine backup.. Any advice as to what my next step should be will be greatly appreciated.
Bud D