problem with ComboBox

<ajaxToolkit:ComboBox ID="drp_LastupdatedTime" runat="server" Width="40px" AutoPostBack="False"
DropDownStyle="DropDown" AutoCompleteMode="SuggestAppend" CaseSensitive="False"
ItemInsertLocation="OrdinalText">
<asp:ListItem Value="0">All</asp:ListItem>
<asp:ListItem>1</asp:ListItem>
<asp:ListItem>3</asp:ListItem>
<asp:ListItem>6</asp:ListItem>
<asp:ListItem>12</asp:ListItem>
<asp:ListItem>24</asp:ListItem>
<asp:ListItem>48</asp:ListItem>
<asp:ListItem>>84</asp:ListItem>
<asp:ListItem>>96</asp:ListItem>
<asp:ListItem>>108</asp:ListItem>
<asp:ListItem>>120</asp:ListItem>
</ajaxToolkit:ComboBox>

its not working properly when page post back.

its looking like textbox and when we send to server its not refresh its value