问ssh登陆不上云服务器了？

  The host 'ip' is unreachable.

     the host may be down,or there may be a problem with the network connection.

    Sometimes such problems can also be caused by a misconfigured firewall。

昨天还是好好的、今天登陆就出现了这个错误，网上都说是没有启动service sshd start 这个，但是我都进不去，怎么启动呢？？？