modalpopupextender vanishes instantly after clicking

As soon as you click the button, the 4 textboxes popup for a brief moment and then immediately vanish. What is causing this to happen? It is supposed to stay there until the close button is clicked;

<%@ Page Title="" Language="VB" MasterPageFile="~/templates/default.master" AutoEventWireup="false" CodeFile="Default2.aspx.vb" Inherits="Default2" %><%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %><asp:Content ID="Content1" ContentPlaceHolderID="head" runat="Server"><title>Create Login ID | MortgageLoanApply.com</title><meta name="description" content="Pacific West Capital" /><meta name="keywords" content="Registration, Create login" /><style type="text/css">
        .modalBackground {
            background-color: transparent;
            filter: alpha(opacity=90);
            opacity: 0.8;
        }

        .modalPopup {
            background-color: white;
            border-width: 3px;
            border-style: solid;
            border-color: black;
            padding-top: 1px;
            padding-left: 10px;
            padding-right: 10px;
            width: 185px;
            height: 160px;
            position: absolute;
            top: 180px;
            left: 350px;
        }
    </style><script type="text/javascript">$(document).ready(function () {$("btnSubmit").click(function () {
                //var x = document.getElementById("alerttype");
                //var y = document.getElementById("alertreason");
                alert("Value: " + $("#alerttype").val());
            });
        });</script></asp:Content><asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceholder1" runat="Server"><div id="menu" class="container"><ul><li><a href="default.aspx">Home</a></li><li><a href="features.aspx">Features</a></li><li><a href="pricing.aspx">Pricing</a></li><li><a href="login.aspx">Login</a></li><li class="current_page_item"><a href="register.aspx">Register</a></li><li><a href="contact.aspx">Contact</a></li></ul></div></asp:Content><asp:Content ID="Content3" ContentPlaceHolderID="ContentPlaceholder2" runat="Server"><asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager><!-- ModalPopupExtender --><cc1:ModalPopupExtender ID="mp1" runat="server" PopupControlID="Panel1" TargetControlID="BtnShow"
        CancelControlID="btnClose" BackgroundCssClass="modalBackground"></cc1:ModalPopupExtender><asp:Panel ID="Panel1" runat="server" CssClass="modalPopup" align="center" Style="display: none"><asp:Label ID="Label7" runat="server" Text="MortgageLoanApply.com - Terms of Service"
            ForeColor="#FFB30F" Font-Size="Large" Font-Bold="True"></asp:Label><div style="height: 60px"><asp:UpdatePanel ID="UpdatePanel1" runat="server"><ContentTemplate><asp:TextBox ID="TextBox1" runat="server"></asp:TextBox><asp:TextBox ID="TextBox2" runat="server"></asp:TextBox><asp:TextBox ID="TextBox3" runat="server"></asp:TextBox><asp:TextBox ID="TextBox4" runat="server"></asp:TextBox></ContentTemplate></asp:UpdatePanel></div><asp:Button ID="btnClose" runat="server" Text="Close" /></asp:Panel><!-- ModalPopupExtender --><asp:Button ID="BtnShow" runat="server" Text="Fee Split" /></asp:Content>