All pages white but homepage after firewall is enabled

Hello d1000,
During the configuration process you should have been prompted to download a backup of .htaccess. If you did that, you can try replacing .htaccess in your root folder with the backup .htaccess

If this doesn’t work you’ll have to check the error logs on your server for more information. These are usually available via the web hosts administration panel. Feel free to share any errors with me if you need help interpreting them.