提交时忘记密码会导致空白页面

I am having an issue with my forgot password page. When i enter in my email address and click submit i am brought to a blank page and an email with my password is not sent. Any help is appreciated. Thanks!

<?php
include 'db.php';
if(isset($_POST['submit']))
{ 
    $email_address=$_POST['email_address'];
    $q=mysql_query("select * from login where email_address='".$email_address."' ") or die(mysql_error());
    $p=mysql_affected_rows();
    if($p!=0) 
    {
        $res=mysql_fetch_array($q);
        $to=$res['email_address'];
        $subject='YNAGS Password Recovery';
        $message='Your password : '.$res['password']; 
        $headers='From:password_reset@ynags.com';
        $m=mail($to,$subject,$message,$headers);
        if($m)
        {
            echo'Check your inbox in mail';
        }
        else
        {
            echo'mail is not send';
        }
    }
    else
    {
        echo'You entered mail id is not present';
    }
}
?>

I am not quite sure what this is here:

$q=mysql_query("select * from login where email_address='".$email_address."' ") or die(mysql_error());

mainly the login part of this statement.

1. We should know the code from db.php (obviously without the sensitive data).
2. Try something like this:
db.php

<?php
define("HOST", "your host");
define("USER", "db user name");
define("NAME", "db name");
define("PASSWORD", "password");
?>

forgot.php

<?php 
include("db.php");
if(isset($_POST['email_address'])){
    $email_address = $_POST['email_address'];
    $con = mysqli_connect(HOST, USER, PASSWORD, NAME);
    $sql = "SELECT * FROM login WHERE email_address = '".$email_address."'";
    if(mysqli_affected_rows(mysqli_query($con, $sql)) != 0){
        $res = array();
        $res = mysqli_fetch_array(mysqli_query($con, $sql));
        $to = $res['email_address'];
        // and so on ...
    }else{
        echo "Email not found";
    }
}else{
    echo "Form not submitted";
}
?>