Hi
Open a new blank project, then try to get the old corrupt project to open from the FCP File menu Open command.
If it does then Copy any Sequences that can be opened to a new Sequence in the new project.
Most likely a Sequence may not open or crash everything.
In which case repeat the procedure, but maybe you can Export a QT movie from that dodgy Sequence without opening it (or from part of it with Sequence In/Outs set). That would give you a record of your edit decisions, if you have to bring an old project up to date.
But! Somewhere in your movie or still assets you’ve probably got a corrupted QT file, or still image.
Working your way through all your captured movie with QT Player may show you which one it is. Ditto Photoshop for stills.
If you find anything dodgy trashing it may allow you to be able to open your corrupt project far enough for the Copy-into-New-Project strategy to work.
Last time it happened to me was in a QT movie made by using Macromedia Director to export its animation to QT. Reexporting/recompressing that dodgy movie in QT Player Pro recovered it for me.