I added the error reporting...still doesn't show up what the problem was. This is the code in my index.php
As you can see, I added some sort of alert if the user_ok returns...which does...
<?php error_reporting(E_ALL); ?>
<html>
<head>
<script language="javascript" type="text/javascript" src="./js/jquery.min.js"></script>
<script language="javascript" type="text/javascript" src="./js/ajax.js"></script>
<script language="javascript" type="text/javascript" src="./js/main.js"></script>
<title>Title</title>
</head>
<body>
<center>
<?php include_once("check-login.php"); ?>
<?php // if ($user_ok == true) { echo "true"; } ?>
<?php if ($user_ok == true): ?>
<div>
<img src='./img/logo.png'><br>
<form action='#' method='post'>
<input type='text' maxlength='88' placeholder='Search'>
</form>
</div>
<?php else: ?>
<div>
<img src='./img/logo-horizontal.png'><br>
<div>
<!-- SOME CONTENT -->
</div>
</div>
<? endif; ?>
</body>
</html>