C#做的网页再打开找不到视图设计器

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>无标题页</title>
    <style type="text/css">
        .style1
        {
            width: 100%;
        }
    </style>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    
        <table class="style1">
            <tr>
                <td>
                    <asp:Label ID="labelEvent" runat="server" Text="Event:"></asp:Label>
                </td>
                <td>
                    <asp:DropDownList ID="dropDownListEvents" runat="server">
                        <asp:ListItem>SQL Server 2005 and XML</asp:ListItem>
                        <asp:ListItem>Office 2003 and XML</asp:ListItem>
                        <asp:ListItem>Introduction to ASP.NET</asp:ListItem>
                    </asp:DropDownList>
                </td>
            </tr>
            <tr>
                <td>
                    <asp:Label ID="labelFirstname" runat="server" Text="Firstname:"></asp:Label>
                </td>
                <td>
                    <asp:TextBox ID="textFirstname" runat="server"></asp:TextBox>
                </td>
            </tr>
            <tr>
                <td>
                    <asp:Label ID="labelLastname" runat="server" Text="Lastname:"></asp:Label>
                </td>
                <td>
                    <asp:TextBox ID="textLastname" runat="server" Width="128px"></asp:TextBox>
                </td>
            </tr>
            <tr>
                <td>
                    <asp:Label ID="LabeEmail" runat="server" Text="Email:"></asp:Label>
                </td>
                <td>
                    <asp:TextBox ID="textEmail" runat="server"></asp:TextBox>
                </td>
            </tr>
            <tr>
                <td>
                    &nbsp;</td>
                <td>
                    <asp:Button ID="buttonSubmit" runat="server" Text="Submit" />
                </td>
            </tr>
        </table>
    
    </div>
    </form>
</body>
</html>
这是Dafault.aspx的代码。
设计完表格后，关闭了VS2008.
第二天打开后找不到视图设计器了。
怎么在打开视图设计器，切换到到图形设计界面？