I had to force to quit lightroom cc because the program did not respond now the mac (Yosemite 10.10.5) report me back this :
The Lightroom catalog called " Lightroom 4 Catalog - 2-3-2 " can not be opened because it is already open in another application.
....but LR isn't open yet and I can not access to the catalog. how can I do?
Please open the Activity Monitor and close any ongoing activity related to Lightroom, else reboot the system and try opening the catalog again.
Let us know if that helps.
LR or your Mac crashed leaving a LOCK file which is created when LR is opened. Go to your Catalog file location and Delete the .Lock file then try opening LR to load your catalog.