Ping ping = new Ping();
            PingReply reply = ping.Send("119.75.218.45");//百度IP
            if(reply.Status == IPStatus.Success)
            {
                MessageBox.Show("已联网");
             }
             else
             {
                 MessageBox.Show("未联网");
              }

C#判断电脑是否处于联网状态