Here's a pretty dirty solution that would do the trick. Use this only for temporary purposes. Place this in your themes functions.php (replace the example.com):
if( !is_user_logged_in() AND !in_array( $GLOBALS['pagenow'], array( 'wp-login.php' ) ) ):
header('Location: http://www.example.com/');
exit;
endif;
Then all not logged users are redirected. Probably you have to change these conditions for your needs.
Access the login with
www.example.com/wp-login.php
instead of
www.example.com/wp-admin