You didn't need to open your latest backup catalog. All you needed to do was to delete the lock file that you found. Then your current catalog which has all the images in that would have opened. The lock file is used by the database engine that drives the Lightroom catalog. It is supposed to be deleted whenever Lightroom closes. But sometimes Lightroom doesn't close normally and that file gets left behind so it has to be deleted manually.
Thank you for your reply. Very simple and helpful!
However, I am now a bit lost as my catalog is messed up. I am missing folders in the catalog that I have open. When I helped LR find them on my hard drive, I got a popup question that read, "The selected folder or one of its subfolders is already in Lightroom. Do you want to combine these folders. I clicked "Merge" and then the folder completely disappeared from the list of folders. I still see it in the correct place on my hard drive, but I can't get to it from LR now. I assume those missing folders (and another folder full of pics I imported but now don't see listed in the catalog) are in another catalog as I think I have been working with the backup catalog that I opened at the beginning of this whole mess. Can you help me get everything current and in one catalog again? Thank you.