Link to checkout page does not work:
There may be a php error occurring, add the following code at line of the cart display page:
<?php
error_reporting(E_ALL);
ini_set('display_erros','on');
?>
This should display the error if there is one occurring.
also add that code toi the checkout page so we can see why it is displaying as blank.
can you send a link to your site so I can look into the cart emptying when adding more than one item.