asp.net 关于js脚本的问题，运行之后没有倒数秒数，哪里出错了？！
<%@ Page Language="C#" MasterPageFile="~/MasterFile/login.master" AutoEventWireup="true" CodeFile="login_xszc.aspx.cs" Inherits="WelcomePage_login_xszc" Title="无标题页" %>

<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
  <style type="text/css">
  .style1
  {
  height: 190px;
  width: 984px;
  }
  .style50
  {
  }
  .style51
  {
  height: 51px;
  }
  .style52
  {
  height: 36px;
  }
  .style53
  {
  width: 355px;
  }
  </style>
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder3" Runat="Server">
</asp:Content>
<asp:Content ID="Content3" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
 <table class="style1" style= " border: thin groove #808080; background: 0 0; 
  width:984px; height:275px; " align="center" border="1">
   
  
   
  <tr>
  <td class="style51" align="center"
  style="background-color: #008080; font-size: x-large;" colspan="2">
  新用户注册</td>
  </tr>
  <tr>
  <td class="style53" align="center">
  &nbsp;</td>
  <td class="style50">
  &nbsp;</td>
  </tr>
  <tr>
  <td class="style53" align="center">
  学生名</td>
  <td class="style50" align="center">
  <asp:TextBox ID="TextBox_name" runat="server" Width="166px"></asp:TextBox>
  &nbsp;&nbsp; <asp:LinkButton ID="LinkButton1" runat="server" onclick="LinkButton1_Click">检验用户名</asp:LinkButton></td>
  </tr>
  <tr>
  <td class="style53" align="center">
  密码</td>
  <td class="style50" align="center">
  <asp:TextBox ID="TextBox_mima" runat="server" Width="250px"></asp:TextBox>
  <FONT color="#ff0000">*</td>
  </tr>
  <tr>
  <td class="style53" align="center">
  确认密码</td>
  <td class="style50" align="center">
  <asp:TextBox ID="TextBox_checkmima" runat="server" Width="250px"></asp:TextBox>
  <FONT color="#ff0000">*</td>
  </tr>
  <tr>
  <td class="style53" align="center">
  密码问题</td>
  <td class="style50" align="center">
  <asp:TextBox ID="TextBox_question" run