[roman]

Prueba esto:

Código Delphi [-]
type
  TForm1 = class(TForm)
  private
    procedure WMSysCommand(var Msg: TWMSysCommand); message WM_SYSCOMMAND;
  end;

implementation

procedure TForm1.WMSysCommand(var Msg: TWMSysCommand);
begin
  if Msg.CmdType and $FFF0 <> SC_RESTORE then
    inherited;
end;

// Saludos