Sending account activation link

    <?php
    require "phpMailer/PHPMailer/PHPMailerAutoload.php";
            $mail = new PHPMailer();
    // initializing variables
    $errors = array();

    // connect to the database
    $db = mysqli_connect('localhost', 'servername', 'password', 'gac');

    // REGISTER USER
    if (isset($_POST['reg_user'])) {
      // receive all input values from the form
      $username = mysqli_real_escape_string($db, $_POST['username']);
      $email = mysqli_real_escape_string($db, $_POST['email']);
      $password_1 = mysqli_real_escape_string($db, $_POST['password_1']);
      $password_2 = mysqli_real_escape_string($db, $_POST['password_2']);
      $_SESSION['username'] = $username;
      $_SESSION['success'] = "You are now successfully registered";

      // form validation: ensure that the form is correctly filled ...
      // by adding (array_push()) corresponding error unto $errors array
      if (empty($username)) { array_push($errors, "Username is required"); }
      if (empty($email)) { array_push($errors, "Email is required"); }
      if (empty($password_1) || strlen($password_1)<8) { array_push($errors, "Password is required and must be 8 length in characters"); }

      if ($password_1 !== $password_2) {
        array_push($errors, "The two passwords do not match");
      }

      // first check the database to make sure
      // a user does not already exist with the same username  email
      $user_check_query = "SELECT * FROM registered_users WHERE email='$email' LIMIT 1";
      $result = mysqli_query($db, $user_check_query);
      $user = mysqli_fetch_assoc($result);

      if ($user) { // if user exists
       /* if ($user['username'] === $username) {
          array_push($errors, "Username already exists");
        }*/

        if ($user['email'] === $email) {
          array_push($errors, "email already exists");
        }
      }

      // Finally, register user if there are no errors in the form
      if (count($errors) == 0) {

          $v_key = md5($email.time());//generate the vkey for database
         $v_addKey = substr(md5(uniqid(rand(),1)),3,8);
            $v_key = $v_addKey.$v_key;

        $password = md5($password_1);//encrypt the password before saving in the database

        //making expiry link for activation of account
         $exp_acc_act_Format = mktime(
       date("H")+1, date("i"), date("s"), date("m") ,date("d"), date("Y")
       );
       $expHour = date("Y-m-d H:i:s",$exp_acc_act_Format);


        $query = "INSERT INTO registered_users (username, email, password, status, v_key, expHour)  VALUES('$username', '$email', '$password',0,'$v_key','$expHour')";

        $insert = mysqli_query($db, $query);
        if($insert)// after insert send verification email
        {
            $output='<p>Dear user,</p>';
    $output.='
    <p>Please click on the following button to activate your account.</p>';

    $output.='<center style ="border:1px solid black;height:40px;width:200px;background-color:#005b2d;">
    <p>
    <a href="http://www.sanjeevsanthalia.com/thankyou.php?v_key='.$v_key.'&email='.$email.'&action=reset" target="_blank" style ="color:white;text-decoration:none;">
    <strong>
    Click here to verify the email
    </strong>
    </a>
    </p>
    </center>';
    $output.='<p>Thanks,</p>';
    $body = $output;
    $subject = "Account Activation -GACKONNECT ";
    $email_to = $email;
    $fromserver = "noreply@gacons.com";
    //$mail->IsSMTP();/*by commenting also it was working*/
    $mail->SMTPAuth = true;
    $mail->SMTPSecure = 'ssl';
    $mail->Host = "hello.com"; // Enter your host here
    $mail->Port = 465;
    $mail->Username = "noreply@hello.com"; // Enter your email here
    $mail->Password = "password"; //Enter your password here
    $mail->IsHTML(true);
    $mail->From = "noreply@hello.com";
    $mail->FromName = "GACKONNECT";
    $mail->Sender = $fromserver; // indicates ReturnPath header
    $mail->Subject = $subject;
    $mail->Body = $body;
    $mail->AddAddress($email_to);

    if(!$mail->send()){
    echo "Mailer Error: " . $mail->ErrorInfo;
    }else{
        header('location:afterRegistration.php');

        }

        }
      }
    }

It was working but suddenly stopped. I am not able to figure out. Receiving data in database also only mail is not sending.