I guess it depends on what the reason of the problem is. If there was a PHP problem, it should give an error.
Try adding this to the top of the script and see if any errors appear:
Yesterday, the first time I clicked those links, I actually saw the second page as well (although the CSS seemed to be totally different from the first page), but when looking at its HTML code there was none. Very strange.
<?php error_reporting(-1); ?>
<?php ini_set('display_errors', true); ?>
But only once, because after that I I'm only getting empty page.