I dont enable a one div from another div

Here is my simple code:

  In code behind:
  protected void Timer1_Tick(object sender, EventArgs e)
  {
 
  DateTime dt = DateTime.Now;
  TimeSpan differ;
  System.DateTime date1 = new System.DateTime(2015, 4, 1, 20, 10, 0);
  differ = date1.Subtract(dt);
  double t = differ.TotalSeconds;

  if (t > 0)
  {
  double dy, h, m, s;
  dy = differ.Days;
  h = differ.Hours;
  m = differ.Minutes;
  s = differ.Seconds;
  Label13.Text = dy.ToString();// +" Days " + h + " Hours " + m + " Minutes " + s + " Seconds left for celebration";
  Label14.Text = h.ToString();
  Label15.Text = m.ToString();
  Label16.Text = s.ToString();
  }
  else
  {
  Timer1.Enabled = false;
  time_enable.Visible = false;
  theDiv1.Visible = true;
  }
  }
 My question is that i visible thDiv1 div from Time1_tick(). But thDiv1 is not visible. How i will do?