Install Unable to SSH after Centminmod install On Google Cloud server

That is how I am doing this by have one public key on the server and private key on putty on my laptop. Never had any problem of this sort before. Still this method is working very well on other stacks but this is happening on centminmod from some days now but I am good considering that this thing actually boosts up my security so its all right. I can keep the key secure, there is no issue with that and now I know how to manually add user and public key onto the server for SSH so its all good now.
Thanks a lot for your help @eva2000

---