Pages work, Posts don't

Hi,
First of all, I’m totally new to WordPress so please be patient ??

Anyway, I have created a custom theme with a bunch of pages, a menu and a startpage (index.php), and everything is working fine. I have also created a few posts and those are not working at all. I have created a small loop that display the 5 latest posts on the startpage as links with date, and they show up as intended, but if I click on one of the links the startpage just reloads. As the page has reloaded it displays the correct permalink in the browser address bar, but I’m still stuck on the startpage. Same if I try to preview my posts from WP-admin, it just display my start page.

I have no idea what I’m doing wrong here and I’m no php coder. This is the code I have in my page.php file, maybe there is something wrong with it?

<?php get_header(); ?>
  <div class="content">
    <?php while ( have_posts() ) : the_post(); the_content(); endwhile; // THE LOOP ?>
  </div>
<?php get_footer(); ?>