500 Internal Server Error messages on every page are typically an indication of a misconfigured site configuration file - such as a .htaccess or web.config file in your hosting package. If you've recently made changes to either of these files, it's worth trying reverting to a previous version.

Common errors include attempting to use php_value directives in your .htaccess file (this won't work on our platform as we run PHP as a CGI - use a php.ini file instead), and incorrect cases in web.config directives.

If you're on Windows hosting, don't forget to recycle the application pool after making changes to your site or configuration, and as the first action to take if you're seeing 500 errors - you can do this via Online Control Panel > Manage IIS Application Pools. You can also see behind the friendly IIS errors - in Online Control Panel > Log File Download, the error message viewer will show you the actual error being generated - this will often point to the location of the error.

It is also worth examining the last few lines of your error logs, as very often, PHP and Apache errors will be logged there. This is to be found in Online Control Panel > Log File Download.