cannot hide modal pop up in content page..

Hi all, 
I'm working on a content page, and I am trying to pop up some windows using ajax modal popup extender , I want to hide and show the popup manually so I us the below code

<asp:Button ID="Button4" runat="server" Text="Button" CausesValidation="False" Style="display: none" /> <cc1:ModalPopupExtender ID="MPmsg1" runat="server" PopupControlID="Panel4" TargetControlID="Button4" CancelControlID="btnmsg1Cancel" BackgroundCssClass="modalBackground" DropShadow="true"> </cc1:ModalPopupExtender> <asp:Panel ID="Panel4" runat="server" CssClass="modalPopup4" align="center"> <asp:Panel ID="Panel8" runat="server" CssClass="mpHd" Height="30px"> &nbsp;&nbsp; <asp:Label ID="Label4 ...