The first thing to check is the user rights to the external drive, using Finder.
Check the drive rights, then the folder rights, subfolder rights, and finally the file rights.
You need READ and WRITE access to everything.
I should have mentioned that I already did this. I have R/W rights for everyone. Thanks
... and it will not let me create a new catalog (If I click on New Catalog, nothing happens).
What do you mean it will not let you create a new catalog? Do you get a dialog box? Do you get an error message?
I am able to switch to other catalogs but they too do not show any folders in the Folder panel.
This seems to me to be an entirely different issue, can you show us a screen capture?
At this point, I have deleted all of my LR preference files. I have uninstalled and re downloaded LR. I have launched it with the Shift + Option keys held down to reset all preferences, and I have disconnected the drive with any LR files on it. I was able to choose the startup option to use the default catalog and open the program. But still when I click on Preferences, Nothing happens. When I click on New Catalog, nothing happens. There is no screen shot to show. I can click on Catalog Settings and it shows me that my catalog is at /users/ken/lightroom. And Open Catalog will allow me to search for existing catalogs. But Preferences or New Catalog do absolutely nothing.
Nothing has changed on my system other than that I disconnected an external hard drive that was failing.
I solved the problem, though I'm not sure why this mattered. My "Pictures" folder was a symbolic link to a directory that non longer exists. My Catalog is not in that folder but, apparently LR was not happy. So I restored the Pictures folder and all seems OK again.