how to detect active window using C#

<script type="text/javascript">
       $(document).ready(function () {
           $(".Display").fancybox({
               'padding': 0,
               'width': 600,
               'height': 200,
               'autoScale': true,
               'transitionIn': 'none',
               'transitionOut': 'none',
               'type': 'iframe',
               'scrolling': 'no',
               'hideOnOverlayClick': false,
               'showCloseButton': true
           });
       });
   </script>

<a class="Display" href='<%# String.Format("UpdateDifferences.aspx?RegNo={0}&Status={1}&FileDate={2}", Eval("RegNo") , Eval("Status") , Eval("File_Date")) %>'><asp:ImageButton ID="imgView" Visible="true" runat="server"
                       ToolTip="Edit" ImageUrl="~/images/Edit.png"
                       Width="20" Height="20" />  
                     </a>

from PageA Invoking PageB(fancybox) 1s update is done i want to close the PageB(fancybox), once pageB is closed automatically PageA will get active, on 
active i want to refresh the pageA.