amtik is correct in looking at the code that needs to be addressed.
Order deny,allow
Deny from all
<Files ~ ".(xml|css|jpe?g|png|gif|js)$">
Allow from all
</Files>
That code was originally only designed to be used in wp-includes and wp-content not in the root of your WordPress install, but even then it will still break themes and plugins. Plus it would be better written like so:
Order Allow,Deny
<FilesMatch "\.(xml|css|jpe?g|png|gif|js)$">
Allow from all
</FilesMatch>
But it would need to go in an .htaccess file in your wp-includes and wp-content directories. I would suggest you just remove it completely and see if your site works. Then create new .htaccess files with the above content for your wp-includes and wp-content directories and see if anything breaks. There’s a good likelihood that something will break it just depends if the user’s browser needs something from those directories.