php file not running when called from xmlhttprequest - php

Question

I am having trouble with my php file (login.php) running when called by javascript using XMLHttpRequest. The php file works fine when I run it from the url, but does not seem to be called by the XMLHttpRequest. I'm new to this and am struggling to get this working.
The javascript file just gets the username and password and sends them as parameters to the php file in the url. The Php file logs check with the database for a correct combination.
My Javascript file:
function logIn(){
if (window.XMLHttpRequest)
{
xmlhttp = new XMLHttpRequest();
}
var usename = document.getElementById("userName").value;
var password = document.getElementById("password").value;
var url = "login.php?q=" + usename + "&x=" + password;
xmlhttp.open("POST", url, false);
xmlhttp.setRequestHeader('Content-Type','application/x-www-form-urlenclosed');
xmlhttp.onreadystatechange = function() {
if (xmlhttp.readyState == 4){
alert("GOOD");
}}
xmlhttp.send(url);
alert(url + xmlhttp.status);
}
function logInClick(){
logIn();
}
window.onload = function() {
document.getElementById("AboutMe").onclick=aboutMessage;
document.getElementById("ContactMe").onclick=contactMessage;
document.getElementById("submitButton").onclick=logInClick;
}
My Php file:
<?php
$host="localhost";
$username="root";
$password="";
$db_name="website";
$tbl_name="users";
mysql_connect("$host","$username","$password")or die("Cannot Connect");
mysql_select_db("$db_name")or die("Cannot Select DB");
$inputUserID=$_POST['q'];
$inputPassword=$_POST['x'];
//$encrpytedPassword=md5($inputPassword);
$inputUserID = stripslashes($inputUserID);
$inputPassword = stripslashes($inputPassword);
$inputUserID = mysql_real_escape_string($inputUserID);
$inputPassword = mysql_real_escape_string($inputPassword);
$sql = "SELECT * FROM $tbl_name WHERE userID='$inputUserID' and Password='$inputPassword'";
$result=mysql_query($sql);
$count=mysql_num_rows($result);
if ($count==1){
session_start();
$_SESSION['userID']=$inputUserID;
//change this at some point
header("location:regularUserLoggedIn.html");
} else {
header("location:www.yahoo.com");
}
?>
Any help would be great. Thanks.

Answer 1

The first line of your PHP Script is header. The execution of the script is stopped after header. Try removing that line and just echo what you get at the server first..

Answer 2

The first line of your php code redirects to another page. The result of the javascript returns will be the redirected page content rather than the outputted content of your code.
P.S. Your javascript code has security issues that others can steal the passwords easily.