How to disable a Parent window when the Child pop-up window opens in C#.net

My Code:

using System;

using System.Data;

using System.Configuration;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Web.UI.HtmlControls;

using System.Data.SqlClient;

public partial class _Default : System.Web.UI.Page

{

dbUtils dbu = new dbUtils();

//SqlDataAdapter dataAdapter;

//DataSet dSet;

//SqlCommand cmd;

//int value;

//string Temp,var;

protected void Page_Load(object sender, EventArgs e)

{

if (Page.IsPostBack == false)

{

session();

}

 

 

}

public void session()

{

if (Session["sess"] == null)

{

string popupWindow = null;

string testScript = "window.open('Default2.aspx','win','width=500,height=200,scrollbars= yes')";

string scriptID = "popup";

string myScript = buildScript(scriptID, testScript);

if (!Page.IsStartupScriptRegistered(scriptID))

{

Page.RegisterStartupScript(scriptID, myScript);

}

}

}

string buildScript(string id, string output_page)

{

string myScript = " ";

myScript += "