Post thumbnails not being displayed

I am working on a custom loop that do what i need expect for one thing i.e to display thumbnails next to each post. i am new but now its really fustrating to try so much.i must be doing something wrong. pls help

  'orderby' =>'parent',
  'order' =>'asc',
  'post_type' =>'page',
  'post__in' => array(8,14,17,19,21,23,25,27),
   $page_query = new WP_Query($args);?>
<?php while ($page_query->have_posts()) : $page_query->the_post(); ?>
   <div class="blocks">
           <div class="imgHolder">
               <?php if(has_post_thumbnail($page_query->post->ID)):
                        echo get_the_post_thumbnail();
            <h1><?php the_title();?></a></h1>
            <p><?php the_excerpt(); ?></p>
<?php endwhile; ?>

is this problem in your blog only on the server hosting or in all other sites it use wp ?!

i m creating a custom loop. i am doing something wrong or missing something