If you are receiving a 500 Internal Server error, it is usually due to one of the following:
1) Some code in your .htaccess file is incorrect
Try renaming your .htaccess to htaccess.old If you no longer receive the error, you can fix the code and rename back to .htaccess
2) Your PHP version is too high for your script or plugin.
Try updating your scripts or plugins or try changing your PHP version from cPanel
3) Some incorrect PHP code in your pages.
Check the file "error_log" in the corresponding folder for any PHP errors.