Unable to view the TabControls when the Page Loads

<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<asp:ScriptManager ID="scriptMgr" runat="server"></asp:ScriptManager>
<asp:TabContainer ID="TabContainer1" runat="server" Width="100%"
ActiveTabIndex="0">
<asp:TabPanel ID="TabbPnl1" runat="server">
<HeaderTemplate>View User Trace</HeaderTemplate>
<ContentTemplate>
<asp:Panel ID="pnlMain" runat="server">
<asp:TextBox ID="txt" runat="server" Text="dsds"></asp:TextBox>
</asp:Panel>
</ContentTemplate>
</asp:TabPanel>

<asp:TabPanel ID="TabPanel1" runat="server">
<HeaderTemplate>View User Trace2</HeaderTemplate>
<ContentTemplate>
<asp:Panel ID="Panel1" runat="server">
<asp:TextBox ID="TextBox1" runat="server" Text="dsds"></asp:TextBox>
</asp:Panel>
</ContentTemplate>
</asp:TabPanel>

</asp:TabContainer>

</asp:Content>