Apache2 configuration only execute PHP partially - php

Question

I am experiencing trouble while installing Apache2 on my Debian 8 VPS (jessie).
I installed the website correctly on Hostinger, it works perfectly, but knowing Hostinger was a free plan, I moved to a sufficient VPS so I could get my hands dirty and do the job my myself. I now can handle everything, but the truth is, it's been a long time since I didn't use a debian server, and installing Apache seems harder than I thought.
So, I secured my VPS as I wanted, that's not the problem, the site works correctly, but partially.
I mean, on somes pages, the PHP code executes very well, it works with my database without any problem. I have a utils.php file that contains a getBDD() function like this one :
return new PDO("mysql:host=localhost;dbname=name;charset=utf8", "user", "password");
And it works on my main pages, I can request everything. You can see it here : http://mdjfeelzor.ovh/petiteancienne.php (the website is french).
But I also have an ajax chat that needs a bit of PHP to work properly. Aaaand I don't understand why, but when I initialize my $conn with getBDD(), I am experiencing an issue further in the code.
Look at that code :
include '../utils.php';
session_start();
if(isset($_POST['enter'])){
if($_POST['name'] != ""){
$_SESSION['name'] = stripslashes(htmlspecialchars($_POST['name']));
try {
$conn = getBDD();
$answer = $conn->prepare('SELECT * FROM openchats WHERE ip=? AND name=?');
$answer->execute(array(stripslashes(htmlspecialchars($_SERVER['REMOTE_ADDR'])),
stripslashes(htmlspecialchars($_SESSION['name']))));
if (!($data = $answer->fetch())) {
$req = $conn->prepare('INSERT INTO openchats (ip, name) VALUES (:ip, :name)');
$req->execute(array(
'ip' => stripslashes(htmlspecialchars($_SERVER['REMOTE_ADDR'])),
'name' => stripslashes(htmlspecialchars($_SESSION['name']))));
}
}
catch(PDOException $e) {
echo "Connection failed: " . $e->getMessage();
}
}
}
It works correctly, right ? (it's supposed to work correctly on your machine) But the thing is, the code starts showing on my web page on the first call of prepare() as you can see here : http://mdjfeelzor.ovh/chat
So, I was wondering, what do you think is the problem ? Is it my way of programming that isn't working ? By the way, I'm using PHP5. I also tried the code <?php phpinfo(); ?> it works perfectly.
Thanks for your help !
EDIT : By the way, the code is shown but it is not supposed to enter in the condition, as $_POST['enter'] doesn't exist on the first load, the code really works on my computer and on Hostinger so I think that the problem comes from Apache configuration ^^' and the AJAX code is not running at that point.