google map API not working.....

hey m trying to embed Google Map API, i hav obtained key for this nd write the following code still it is not displayng map.......please help

<%@ Page Language="C#" MasterPageFile="~/nationalmaster.master" AutoEventWireup="true" CodeFile="contactus.aspx.cs" Inherits="contactus" Title="::contact us::" %>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">

<script type ="text/javascript" language ="javascript">
function initialize()
{
  var mapProp = {
    center: new google.maps.LatLng(51.508742,-0.120850),
    zoom:7,
    mapTypeId: google.maps.MapTypeId.ROADMAP
  };
  var map = new google.maps.Map(document.getElementById("googleMap"),mapProp);
}
function loadScript()
{
  var script = document.createElement("script");
  script.type = "text/javascript";
  script.src = "http://maps.googleapis.com/maps/api/js?key=AIzaShjutjI1U1gggksyutyrbtgsQq8hCqerwdhhfjdxs7ZuPcM&sensor=false&callback=initialize";
  document.body.appendChild(script);
}
</script>
<div class ="googlemap" style =" width :500px ; height :500px">
    <asp:Button ID="Button1" runat="server" OnClientClick ="return loadScript();" Text="view map" /></div>
</asp:Content>