I would simplify it:
Move ALL your Events/Projects out of the FCPX folders, into some other, say 'FCPX Events OFF' & 'FCPX Projects OFF'.
Then move ONE event/projects back at a time, localizing the problematic event or project.
And note: you don't have to move event AND projects together! You can start with all the events, and then take projects last.
Then, at least, you should be able to localize the problematic event/project, and restore to an earlier version, minimizing your loss..
Try Digital rebellions tool,
they have a trial version, 15 days, I think you will find that this may work for you.
Two things that may cause this
Corrupt render files, solution, delete the render files in your projects.
Corrupt media files, Pro maintenance Tool
Also, try launching the event without the projects, this will let you know which is causing the problem, event or project.
let us know how you go.