If you have just setup your Joomla website or if you have recently performed an upgrade and you now get an "Internal Server Error 500" when you open your web site, check this article for a possible solution of this problem.
A fresh Joomla install includes a file called .htaccess, which is located in the main folder of your Joomla installation. This file contains certain configuration settings, which may get in conflict with the current web server configuration. The result would be an Internal Server Error 500 displayed whenever you try to view your website.
You can quickly determine whether it is the .htaccess file that is causing the error by renaming it to a .htaccess (thus disabling it). Should this resolve the error, you would at least know where to look for the exact cause of the problem. It must be one of the directives within the .htaccess file, so it would only a matter of finding our one it is and removing it (or commenting it).
Open the .htaccess file with a plain text editor – you can edit it via the File Manager (Site Management> File Manager) on your web hosting control panel. Look for this line:
Options + FollowSymLinks
If you see it, put a # in front of it, so it would look like this:
#Options + FollowSymLinks
FollowSymLinks are enabled by default, so rest assured that you do not cripple your Joomla installation in any way by disabling this directive. This should fix the Internal Server Error 500 problem. If it does not try commenting other directives until you find out which one is causing the problem – any of the following would cause problems: Options, phpflag, ExecCGI, FollowSymLinks, Includes.