为什么PHP包含不起作用？

I'm trying to make a page view counter. I'm a newbie to PHP. Here is my problem: I'm using this code in "index.php":

<?php
    include "visitcounter.php";
?>

And using the following code in "visitcounter.php":

<?php
session_start();
if(isset($_SESSION['visitcount']) {
    $_SESSION['visitcount'] = $_SESSION['visitcount']+1;
} else {
    $_SESSION['visitcount'] = 1;
}

echo "Total Page Views = ".$_SESSION['visitcount'];

?>

The problem is the page index.php is showing server error. If I change the code with the following code in index.php:

<?php
    include "/visitcounter.php";
?>

Then the page not show any error message but display nothing. Anyone please help me to figure out what is the wrong I'm doing.

First of all, the point mentioned of Silvio Silva is the problem.

Change from:

session_start()

to:

session_start();

To avoid such problems in future, just add to the file:

ini_set("display_errors","on");
error_reporting(E_ALL);

This will show you such errors then directly in the output, so that you can find it easier.