after submitting form in php, success message modal not loading

<?php 
if(isset($_POST['submit'])){

    $to = "contact@solutions.com"; // this is your Email address
    $from = $_POST['name1']; // this is the sender's Email address
    $first_name = $_POST['name2'];
    $last_name = $_POST['email2'];
    $last_name1 = $_POST['number1'];
    $subject = "Referal";
    $subject2 = "Bolster Referal.";
    $message = $from . " has refered the following student :" . "\n\n" . $first_name. "\n\n" .$last_name. "\n\n" .$last_name1;
    $message2 = "Your friend " . $from . " has refered you to us" ;

    $headers = "From:" . $from;
    $headers2 = "From:" . $to;
    mail($to,$subject,$message,$headers);
    mail($last_name,$subject2,$message2,$headers2); // sends a copy of the message to the sender
    //echo "Mail Sent. Thank you " . $first_name . ", we will contact you shortly.";
    // You can also use header('Location: thank_you.php'); to redirect to another page.
    echo "<script>
         $(window).load(function(){
             $('#thankyouModal').modal('show');
         });</script>";
    }
?>

<div class="modal fade" id="thankyouModal" tabindex="-1" role="dialog"><div class="modal-dialog"><div class="modal-content"><div class="modal-header"><button type="button" class="close" data-dismiss="modal" aria-hidden="true">&times;</button><h4 class="modal-title" id="myModalLabel">Thank you for pre-registering!</h4></div><div class="modal-body"><p>Thanks for getting in touch!</p></div></div></div></div>