I took a look at your .htaccess and the .backups you had, since WP usually doesn't die like that.
At the bottom of your .htaccess.bak I saw this:
# END WordPress
BEGIN Visitor Maps Extended
# BEGIN banned ips
<Limit GET POST>
deny from IP
allow from all
# END banned ips
# END Visitor Maps Extended
The problem was likely "BEGIN Visitor Maps Extended" which was not commented out.
By the way, you should have that deny section put above the WordPress one It'll help your site run faster, by punting those IPs before processing any WP files.