If I understood you correctly you want to disable all attachment pages and redirect them to 404 page. Place this code in functions.php and try it again.
add_action( 'template_redirect', 'redirect_media_to_404' );
function redirect_media_to_404() {
if ( is_attachment() ) {
global $wp_query;
$wp_query->set_404();
status_header( 404 );
get_template_part( 404 );
exit();
}
}