One node is down in three node vertica cluster

Hi,

I have installed vertica on three node cluster with k-Safety=1. Out of three, one node is down and other two is up. How can I make one node up and running without disturbing other two nodes.

Also from couple of days, everyday Vertica node is getting in down status or unknown status. And when I am making it up and running, it will work for some time and again it will go down. What will be the reason.

Thanks