Most of the times we get this error "500 internal server error contact your webmaster at firstname.lastname@example.org" in our site.
We don't know what may be the reason Below are some of the things needs to be chacked.
- Check your .htaccess file for any error
- Take a backup and delete the .htaccess file and you came to know whether cause is because of that file
- Check errors in robots.txt file
- Check the sites index.html file for any errors or automatic scripts that your server not supports due to overload
- Do a restore of the settings in cpanel like mime settings etc
- Restart the Apache server by entering in to shell access from your cpanel
If you found more information provide us by comments happy problem solving.