Why do i get a blank page when running this code? [closed]

When i uncomment any one of the commented lines and reload the webpage i end up with a blank page.
If I run the file in the command line the result looks fine.
Do you know where my mistake is?

This is my code:

<?php
   $daten = fopen("statistikpool.txt","a+");
   //$zeile = fgetcsv($daten,100);
   //fclose($daten);
?>
<!DOCTYPE html>
<html>

<body>
The content of the body element is displayed in your browser.
<?php
echo "test";
?>
</body>
</html>