asp.net gridview doesn't display data

protected void Button1_Click1(object sender, EventArgs e)
{
    SqlConnectionStringBuilder connb = new SqlConnectionStringBuilder(ConfigurationManager.ConnectionStrings["SCS"].ConnectionString);      
    using (SqlConnection conn = new SqlConnection(connb.ConnectionString))
    {
        SqlCommand cmd = new SqlCommand("Select * from dbo.Users;", conn);
        DataTable tb = new DataTable();

        SqlDataAdapter da = new SqlDataAdapter(cmd);

        da.Fill(tb);
        tb.AcceptChanges();
        GridView1.DataSource = tb;
        GridView1.DataBind();
     }
}

This is my code in C# asp.net application. I want to display SQL table in gridview.

<Columns>
  <asp:BoundField ItemStyle-Width="150px" DataField="name" HeaderText="name" />
  <asp:BoundField ItemStyle-Width="150px" DataField="lastname" HeaderText="lastname" />
  <asp:BoundField ItemStyle-Width="150px" DataField="ID" HeaderText="ID" />
</Columns>

IT shows empty gridview(When I press button1). It doesn't shows any error message. Connection string works, SQL command affects rows, But it still doesn't show any data on gridview!!!

Can anyone help me?