I deleted the .htaccess file, and then the site worked. But when I click on "Secure Now," I get this message:
"Auto-rollback executed: After writing, the homepage went into a redirect loop (Status 301). The previous state was automatically restored. Most likely, a custom rule you imported (e.g., an old Admin Tools redirect) is conflicting with the Joomla/HTProtect redirect – please remove or adjust that rule."
However, I haven't added any rules to the .htaccess. It's all default. Also, the internal menu links on the site lead nowhere.