The message: "Can not import from this catalog at this time. The catalog is either in use by another copy of Lightroom or was closed improperly. If it was closed improperly, please consider doing an integrity check when opening." indicates that the so-called "lock-file" has not been deleted when your hard drive crashed. The purpose of the lock-file is to prevent that Lr can be opened in one (1) instance only. It should only be present when Lr is open but should not be present while Lr is closed.
In Mac Finder navigate to the location of the catalog that you were trying to open and look if there is a file named < xyz.lrcat.lock>. If present it will sit right next to your catalog <xyz.lrcat>.
Send the file with the suffix .lock to the Trash Can and try to open this catalog again. For convenience you might just double-click the catalog file.