//将该出发语句放main方法下，触发。

SystemEvents.SessionEnding += new SessionEndingEventHandler(SystemEvents_SessionEnding); 

      private static void SystemEvents_SessionEnding(object sender, SessionEndingEventArgs e)
        {             
            SessionEndReasons reason = e.Reason;
            switch (reason)
            {
                case SessionEndReasons.Logoff:
                    //MessageBox.Show("用户正在注销。操作系统继续运行，但启动此应用程序的用户正在注销。");
                    break;
                case SessionEndReasons.SystemShutdown:
                    //MessageBox.Show("操作系统正在关闭。");
                     ...
                     ...
                    break;
            }
        }