How to Fix "500 Internal Server Error" of My WordPress Site?

The most common cause of a 500 Internal Server Error message is a corrupt .htaccess file. Additional causes can be a conflicting plugin or theme, or even a corrupt WordPress installation.

You will need FTP access on your server. Navigate to the root directory of your WordPress installation, and locate the .htaccess file. Rename the file to, let us say, something like .htaccess_old

Now reload your website. If it works, congratulations! You can now generate a new .htaccess file simply by navigating to Setting > Permalinks in your WP admin panel and re-saving the settings.