Simply add orderby to your query_posts
<?php query_posts($query_string . '&cat=-4&orderby=date&order=DESC'); ?>
Update
try:
global $wp_query;
$args = array_merge( $wp_query->query, array('cat' => -4,'orderby' => 'date','order' => 'ASC'));
query_posts( $args );
and if you still get the same change ASC to DESC.