In my case I had moved the site from another server.
In the .htaccess file in public_html there was a section starting
# Wordfence WAF and ending # END Wordfence WAF.
I removed that section from .htaccess and the site came back to life.
I stored a copy of the original .htaccess on my hard drive, just in case.
Went back, deleted Wordfence, then Added it back to the site, and it is good now.
