If your catalog won’t open,
Open Windows File Explorer or Mac Finder and choose the folder where Lightroom stores your catalog,
Check for a ‘your catalog name.lock’ file alongside your catalog file, and delete it, and then try to restart.
The lock file can get left behind if LIGHTROOM crashes, or is not closed correctly, preventing you from opening the catalog.
Do not delete ‘your catalog name.LRCAT’ file, as that is your master catalog of data.
Do not delete ‘your catalog name.LRCAT-journal’ file, as it contains recent information.
I dont have a mac finder and am not sure what you mean by that? I have a PC
You have a PC- ok, then open Windows File Explorer, or open "This PC" or "My Computer" (depending on you OS version)
If you do not know where your catalog is- Use the 'Search' function to find your catalog (and see link below). (Enter *.LRCAT to search for any and all catalogs)
If a "LOCK" file exists it will be found in the same folder as the catalog .LRCAT file.
File Location advice-