Sub menu(Child Menu) not displaying in Main menu(Parent Menu)

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Hi,

My sub menu(Child Menu) not displaying properly in the Main menu(Parent Menu).

see my code
-----------

ASPX Code
---------

<table width="100%" border="0" align="left" cellpadding="0" cellspacing="0" style="height:15;">
	                    <tr>
	                       
                            <td width="100%">
                            <div id="ddtopmenubar" class="mattblackmenu">
                            <ul>
                            <asp:Menu ID="Menu1" Orientation="Horizontal" runat="server"> 
                                    <items> 
                                        <asp:MenuItem Text="Home" Value="First" NavigateUrl="~/Home.aspx"> 
                                         
                                        <asp:MenuItem  Text="Master" Value="Second"> 
                                            <asp:MenuItem  Text="Employee" Value="1" NavigateUrl="~/frmEmp.aspx"> 
                                            <asp:MenuItem Text="Vendor" Value="2" NavigateUrl="~/frmVendor.aspx"> 
                                            <asp:MenuItem Text="contract" Value="3" NavigateUrl="~/frmContract.aspx"> 
                                         
                                        <asp:MenuItem Text="Transaction" Value="Third"> 
                                            <asp:MenuItem Text="Trans1" Value="1"> 
                                         
                                    </items> 
                            
                            </ul>
                            </div>
                         </td>
	                    </tr>
                        
                  </table>  <!--Menu End-->

CSS File
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/* ######### Matt Black Strip Main Menu Bar CSS ######### */
.mattblackmenu ul{
margin: 0;
padding: 0;
font: bold 11px Verdana;
list-style-type: none;
border-bottom: 1px solid red;
filter: progid:DXImageTransform.Microsoft.Gradient(endColorstr='#0A4270', startColorstr='#0A4270', gradientType='0');
overflow: hidden;
width: 100%;
}
.mattblackmenu li{
display: inline;
margin: 0;
}
.mattblackmenu li a
{
	float: left;
	display: block;
	text-decoration: none;
	margin: 0;
	padding: 5px 8px; /*padding inside each tab*/
	border-right: 1px solid red; /*right divider between tabs*/
	color: white;
}.
.mattblackmenu li a:visited{
color: white;
}
.mattblackmenu li a:hover{
background: black; /*background of tabs for hover state */
}
.mattblackmenu a.selected{
background: black; /*background of tab with "selected" class assigned to its LI */
}
/*Modal Popup*/
.modalBackground {
 background-color:Gray; 
 -ms-filter: alpha(opacity=70);
 -ms-opacity:0.7;
}
#nav table { display:inline;} 
#nav tr { display:inline; } 
#nav td { display:inline;} 
#nav a {display:inline;}

What is the problem over here..

Why sub menu is not displaying here....?

pls. help