How to resolve the WordPress Error 500 ?
Most of the time it will be an issue with your .htaccess file. Save it, remove it to check.
If the error 500 persists, that means one of your WordPress file has something wrong with its permission.
Check .htaccess permission attributs. Right click on it : access rights, it should be 644 and not 640.
The same with wp-config.php, it should be 644 and not 640.