Thumbnails not showing up

I've tried searching and followed all the steps but still can't seem to figure this out. I'm trying to pull the last 4 posts from a category and display the title and thumbnail. I'm using this code below but can't get the thumbnails to show up.

<?php query_posts('showposts=4&category=uncategorized');?>
<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>
	<div>
		<h1><?php the_title(); ?></h1>
		<p><?php the_post_thumbnail(); ?></p>
	</div>
<?php endwhile; else: ?><p>Oops, no posts!</p><?php endif; ?>

PHP:

I've replaced "the_post_thumbnail" with "the_content" and "the_excerpt" and the full size images show up.

I've also added this to the "functions.php" but no luck.

add_theme_support( 'post-thumbnails' );
set_post_thumbnail_size( 50, 50, true );

PHP:

How can I get the thumbnails to show up? Any suggestions??? Any help would be greatly appreciated!

 

BTW I'm willing to pay if someone can help me out. I can paypal the money as soon as it's done.