new WP_Query issues

The issue with your query is that new WP_Query($query_string,$args); is not correct syntax, however, creating a new WP_Query is not the way to do what you want. See the codex page for pre_get_posts for the correct way to modify the main query.

I assume by setting posts per page to 999, you want to show all posts, so just use -1 instead to remove the limit from the query. This would go in your theme’s functions.php file:

function wpa90381_category_query( $query ) {
    if ( $query->is_category() && $query->is_main_query() ) {
        $query->set( 'posts_per_page', -1 );
        $query->set( 'orderby', 'name' );
    }
}
add_action( 'pre_get_posts', 'wpa90381_category_query' );