ASP.NET (VB.NET) สอบถามเกี่ยวกับ table สงสัยว่าทำไมไม่อยู่กลาง

        <table border="0" width="800" height="800">
            <tr height="200"><td background="img/head.jpg"  width="800" height="200" valign="top"></td></tr>
            
            <tr height="600" ><td background="img/left.jpg" width="200" align="center" valign="top" ><center>
                <br />
                <br />
                <br />
                <asp:Label ID="Label1" runat="server" Font-Bold="True" Text="ค้นหาหนังสือ ใน Book Store" Font-Size="XX-Large" Width="390px"></asp:Label><br />
                <br />
                &nbsp;<asp:TextBox ID="search" runat="server" Font-Size="Large" Width="378px"></asp:TextBox>
                <br />
                <br />
                <asp:Button ID="Button1" runat="server" Font-Bold="True" Text=":: :: ค้ น ห า :: ::"
                    Width="200px" />
                &nbsp; &nbsp; &nbsp; &nbsp;
                <asp:Button ID="Button2" runat="server" Text=":: :: Clear :: ::" Width="200px" /><br />
                <br />
                &nbsp;&nbsp;
                <asp:GridView ID="ansSearch" runat="server" AutoGenerateColumns="False">
                </asp:GridView>
                &nbsp;
            </center></td>
                
             </tr>
        
        
        </table>