Unable to type in ASP.Net AJAX ComboBox control

I want search the data in combobox .

i am using AutoCompleteMode="SuggestAppend" and DropDownStyle="Simple"

But I can't type any text in combo box

Please any one help me...

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
    CodeFile="Default.aspx.cs" Inherits="_Default" %>
    <%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1"  %>

<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">
</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
<asp:ScriptManager ID="sp1" runat="server"></asp:ScriptManager>
<cc1:ComboBox ID="c1" runat="server" AutoCompleteMode="SuggestAppend" DropDownStyle="Simple"></cc1:ComboBox>
    </asp:Content>

protected void Page_Load(object sender, EventArgs e)
    {
        if (IsPostBack == false)
        {
            bind_dg();
        }
    }
    private void bind_dg()
    {
        string constr = ConfigurationManager.ConnectionStrings["connect"].ConnectionString;
        string query = "select surgery_name from surgery_master  order by surgery_name";
        SqlCommand cmd = new SqlCommand(query);        
        using (SqlConnection con = new SqlConnection(constr))
        {
            using (SqlDataAdapter da = new SqlDataAdapter())
            {
                cmd.Connection = con;
                da.SelectCommand = cmd;
                using (DataTable dt = new DataTable())
                {
                    da.Fill(dt);
                    if (dt.Rows.Count > 0)
                    {
                        for (int i = 0; i < dt.Rows.Count; i++)
                        {
                            c1.Items.Add(dt.Rows[i]["surgery_name"].ToString());

                        }

                    }
                }
            }
        }

    }