Ouvrir et fermer une fenêtre

Voila mon programme:
Code:
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unit WebForm1;
 
interface
 
uses
  System.Collections, System.ComponentModel,
  System.Data, System.Drawing, System.Web, System.Web.SessionState,
  System.Web.UI, System.Web.UI.WebControls, System.Web.UI.HtmlControls,dialogs;
 
type
  TWebForm1 = class(System.Web.UI.Page)
  {$REGION 'Designer Managed Code'}
  strict private
    procedure InitializeComponent;
    procedure Btn_annuler_Click(sender: System.Object; e: System.EventArgs);
    procedure Btn_valider_Click(sender: System.Object; e: System.EventArgs);
  {$ENDREGION}
  strict private
    procedure Page_Load(sender: System.Object; e: System.EventArgs);
  strict protected
    Btn_valider: System.Web.UI.WebControls.Button;
    Btn_annuler: System.Web.UI.WebControls.Button;
    Label1: System.Web.UI.WebControls.Label;
    Label2: System.Web.UI.WebControls.Label;
    Label3: System.Web.UI.WebControls.Label;
    TextBox_identifiant: System.Web.UI.WebControls.TextBox;
    TextBox_mdp: System.Web.UI.WebControls.TextBox;
    Label4: System.Web.UI.WebControls.Label;
    procedure OnInit(e: EventArgs); override;
  private
    { Private Declarations }
  public
    { Public Declarations }
  end;
 
implementation
 
uses sysutils;
 
{$REGION 'Designer Managed Code'}
/// <summary>
/// Required method for Designer support -- do not modify
/// the contents of this method with the code editor.
/// </summary>
procedure TWebForm1.InitializeComponent;
begin
  Include(Self.Btn_valider.Click, Self.Btn_valider_Click);
  Include(Self.Btn_annuler.Click, Self.Btn_annuler_Click);
  Include(Self.Load, Self.Page_Load);
end;
{$ENDREGION}
 
procedure TWebForm1.Page_Load(sender: System.Object; e: System.EventArgs);
begin
  // TODO: Put user code to initialize the page here
end;
 
procedure TWebForm1.OnInit(e: EventArgs);
begin
  //
  // Required for Designer support
  //
  InitializeComponent;
  inherited OnInit(e);
end;
 
procedure TWebForm1.Btn_valider_Click(sender: System.Object; e: System.EventArgs);
begin
if(textbox_identifiant.Text='')then
begin
showmessage('Vous n''avez pas saisi d''identifiant');
end
else
if(textbox_mdp.Text='')then
begin
showmessage('Vous n''avez pas saisi de mot de passe');
end
else
if((textbox_identifiant.Text<>'Admin')or(textbox_mdp.Text<>'admin'))then
begin
   showmessage('Identifiant ou mot de passe non valide');
end
else
showmessage('c''est bon');
end;
 
procedure TWebForm1.Btn_annuler_Click(sender: System.Object; e: System.EventArgs);
begin
end;
end.
J'aimerai que la procedure btn_annuler_click ferme la fenetre et que la procedure btn_valider_click ouvre une nouvelle fenetre.
pourriez vous m'aider?
merci