how to generate a Pop Up?

<asp:HyperLink ID="lnkforgetpwd" href="javascript:openPopup1('ForgetPassword.aspx')" runat="server">Forgot password

function openPopup1(strOpen) {
            open(strOpen, "Forgot Pop UP",
         "status=1, width=400, height=200, top=100, left=300");
        }
</script>

ScriptManager.RegisterStartupScript(this.Page, this.GetType(), "tmp", "<script type='text/javascript'>validatePopup();</script>", false);

function validatePopup()
{
  var txt;
    var r = confirm("your password is sent to your mail");
    if (r == true) {
        this.close();
    } else {
        txt = "You pressed Cancel!";
    }
   
}