single.php in WordPress does not render anything

Question

I have code in my single.php

<?php 
get_header(); ?>

<?php if(have_posts()):  ?>
<?php   while(have_posts()): the_post(); ?>
            <h1><?php the_title(); ?></h1>
            <p><?php the_category(', ');?><?php the_date(); ?> by <?php the_author(); ?></p>
            <div><?php the_content(); ?></div>
<?php   endwhile; ?>    
<?php else:  ?>
<?php   wp_redirect(get_bloginfo('siteurl').'/404', 404); exit; ?>
<?php endif; ?>


<?php 

get_footer(); ?>

but when I launched my site nothing happened. However, when I put this code in index.php everything is displayed as should. Does anyone know what can be problem?