robomongo连接报错Cannot connect to the MongoDB at localhost:27017

用robo连接mongo时，出现下面这种错误，一般是因为Mongodb的服务没有打开，自己在服务中打开或者重启mongoDB服务即可正常连接

Cannot connect to the MongoDB at localhost:27017. Error: Network is unreachable. Reason: couldn't connect to server localhost:27017