Macbook Air没有运行php脚本

can anyone help me out. my macbook air is not running my PHP script. My other computers work fine with it. It does the same thing in every browser I try, Chrome and Safari.

<?php
include_once "connect.php";

session_start();
$username = $_SESSION['user'];
echo $username.'1';
date_default_timezone_set('America/Chicago');
error_reporting(E_ALL);
ini_set("display_errors", 1);
$sql = mysql_query("SELECT * FROM balance_dates where Academy='Old_Cheney'");
while($row = mysql_fetch_array($sql)){
$date0=$row['Date'];
}

$sql = mysql_query("SELECT * FROM starting_ammounts where Academy='Old_Cheney'");
while($row = mysql_fetch_array($sql)){
$date=$row['date'];
}

if($username=='oldcheney'){
    echo $username.'2';
if(strtotime($date0) > strtotime($date)) {
echo $username.'3';}
else {
echo $username.'4';}
}

exit();
?>

its not the cleanest code, sorry, but I would just like to figure out why my macair isn't working with it while my others are. My computer does echo the $username.'1' at the top properly, but not after the if($username=='oldcheney'), which the echo at the top does confirm that it is actually set as oldcheney. Can anyone tell what is wrong? its just frustrating because it works on every other computer I use.