Wordpress Post Thumbnail Issue (Only 1 thumbnail o

I'm using the below code on index.php file of twentyeleven

get_header(); ?>

    <div id="primary">
        <div id="content" role="main">

        <?php if ( have_posts() ) : ?>

            <?php twentyeleven_content_nav( 'nav-above' ); ?>

            <?php query_posts('cat=4&amp;showposts='.get_option('posts_per_page')); ?>

            <?php /* Start the Loop */ ?>
            <?php while ( have_posts() ) : the_post(); ?>
            <div class="post-thumb-title">
            <a href="<?php the_permalink() ?>"><?php the_post_thumbnail(array(632,305));?></a>
            <p class="thumb-title"><?php the_title(); ?></p>
            </div>                  

            <?php endwhile; ?>

            <?php twentyeleven_content_nav( 'nav-below' ); ?>

        <?php else : ?>

            <article id="post-0" class="post no-results not-found">
                <header class="entry-header">
                    <h1 class="entry-title"><?php _e( 'Nothing Found', 'twentyeleven' ); ?></h1>
                </header><!-- .entry-header -->

                <div class="entry-content">
                    <p><?php _e( 'Apologies, but no results were found for the requested archive. Perhaps searching will help find a related post.', 'twentyeleven' ); ?></p>
                    <?php get_search_form(); ?>
                </div><!-- .entry-content -->
            </article><!-- #post-0 -->

        <?php endif; ?>

        </div><!-- #content -->
    </div><!-- #primary -->

<?php get_sidebar(); ?>
<?php get_footer(); ?>

As you can see from the code above, I'm only showing the posts with Cat ID = 4 and I'm using css to overlay the title on the image thumbnail which is generated using the function "the_post_thumbnail" with a custom size. The issue is that the frontpage is only showing the title of the posts and thumbnail only for the 1st post.

You can see the website here: http://fusion.fusionconstruction.co.uk/

Links to other posts with category ID 4 selected:

http://fusion.fusionconstruction.co.uk/fusion-media-at-revolution-round-1/

http://fusion.fusionconstruction.co.uk/fusion-launch-new-website-for-dean-downing/

I would like to display all the posts similar to the 1st one.

Thanks!

<?php query_posts('cat=4&amp;showposts='.get_option('posts_per_page')); ?>

should probably be

<?php query_posts('cat=4&showposts='.get_option('posts_per_page')); ?>

That is, you shouldn't urlencode the ampersand. Hopefully this is what is messing up your query.

Also, the_post_thumbnail() will show the post's featured image, so for it to produce a thumbnail you need to make sure that all the posts have a featured image.