I found a good post with many happy users that were able to get theirs running with this same issue. My computer crashed and I had the files rebuilt from a backup. If I follow the instructions to use %appdata% to find my Managed Catalog.mcat ut that file is not there. I did find a file called Catalog-2.lrcat and one named Assets 1 master.
All my photos show up when I use the web to access them so they are in the Adobe cloud. I need to find a way to clear the file that is blocking Lightroom frame starting without a corrupted file message that causes it to close without access.