Modalpopup on pageload

<AjaxControlToolkit:ModalPopupExtender   runat="server"
                 ID="ModalPopupThanks" TargetControlID="hythanx"
                 PopupControlID="pnlThanks"
                 CancelControlID="Btnthnxok"
                 backgroundcssclass="modalBackground">

              <asp:Panel ID="pnlThanks"  runat="server" CssClass="modalBackground " >
                 <div>
                <!-- ur content here -->
                 </div>
                 <div style="text-align:center "><asp:Button ID="Btnthnxok" runat="server" Text="OK" /></div>

protected void Page_Load(object sender, EventArgs e)
      {
          if (!IsPostBack)
          {
             ModalPopupThanks.Show();


          }

       /* expalian yr needy methods*/
      }