I have installed and re - installed Lightroom but each time I try to open it a bx comes up and says the lighroom catalogue named lightroom catalogue cannot be opened because another application already has it open . quit the other lightroom before trying to launch.
but I don't know how to quit the other light room?
Go to the folder that contains your catalog and look for a file with the lock extension. If you find that file you need to delete it. This is a file that is generated by the Lightroom catalog when it is opened, and it normally is deleted when Lightroom closes. If Lightroom doesn't shut down normally this lock file can be left behind, and that's what causes this problem..