I have just run into an extremely nasty bug (Case 193362) where Unity just crashes on startup leaving three bug report windows behind.
Is there a way to start the editor without loading the last opened project? I have a hope that it will fix my issue (after that I can try to fix my project!)
Hold down option/alt when opening Unity to either create a new Project or open an existing one. 3 simultaneous bug report windows sounds nasty… I’m sure QA will get to your case within a day or two.
It is very nasty… Thanks for the info! That at least got Unity up and running. Now to find out what is wrong with my project!
I got my project back up by copying all assets to a new location and resetting all references. 
Glad it wasn’t that large a project. This is really irritating.
Sounds like Unity QA would be thrilled to get a copy of the project so they can see what was causing the crash.
Please file a bug using the bug reporter and attach the broken project folder with it.
I had that in mind and have just done so. Hope they find the bug so nobody else experiences it. If this had been my project closer to finishing up I would have been very pissed - as it would have taken ages to set up all references again.