Why isn’t my multiple loops working?

by

This seems to work:

while( have_posts() ): the_post();
    the_content();
endwhile;

$my_query = new WP_Query('page_id=40');
while ($my_query->have_posts()) : $my_query->the_post();
    $do_not_duplicate = $post->ID;?>

        <div class="entry">

            <?php the_content('read more &raquo;'); ?>

        </div>

     <?php
endwhile;