Cómo verificar si mod_rewrite está activo en tu servidor
From Joomla! Documentation
Muchos problemas de SEO aparecen cuando un servidor no tiene activo mod_rewrite (en Apache). Puedes verificar si esta configuración es correcta o no y si por este motivo estás teniendo errores HTTP 500.
A continuación el procedimiento para comprobar si mod_rewrite está activo:
1. Activa SEO en el administrador:
Site -> Global Configuration -> SEO Settings: Search Engine Friendly URLs to Yes, Use URL Rewriting to Yes. (Setting Add suffix to URLs is optional).
2. Rename your htaccess.txt to .htaccess:
Next place ONLY the following lines in your .htaccess:
RewriteEngine On
Options +FollowSymLinks
RewriteRule ^joomla\.html http://www.joomla.org/? [R=303,L]
3. Now point your browser to: http://www.example.com/joomla.html
(Replace www.example.com with your own domain name in the URL above.)
If it redirects you to joomla.org then mod_rewrite is working. If it gives you an error then mod_rewrite is not working.
Note: if your site is located in a folder such as "/test/" you need to insert the code in the root .htaccess file as follows:
RewriteEngine On
Options +FollowSymLinks
RewriteRule ^test/joomla\.html http://www.joomla.org/? [R=303,L]