I like Al's theory that a corrupted render file may be the cause. Hopefully, you will be able to select the project icon without crashing the app and from the File folder, Delete Generated Project Files. (Choose All when prompted.) If merely selecting the project crashes the app, select the library and delete its renders.
If you still can't open your working project, but can open new libraries and new projects, open the Final Cut Backups folder, which is typically located in the user's Movie folder. Navigate to the latest tine-stamped library copy that was created prior to your project's developing issues. Double click the library icon and it should open in FCP.
Russ