How I will access to droplet if I loose my private key. I am running Ubuntu 14 and Given "No" to Password Authentication.
Please help me understand that what I have to do if I loose my private Key
You have two options,
if you have a system user with a password set (even though SSH Password Auth is off) then you can use the Web Console to access it, as this is like accessing the server physically and thus only supports passwords.
Your other option is the Recovery Kernel (or Recovery Distro, for which you have to ask Support to enable this for you)
The Recovery Kernel you can enable yourself, you can mount your partitions and add your new Public key using this. Use this guide, for how to enable this kernel, the fsck stuff is unrelated: https://www.digitalocean.com/community/tutorials/how-to-recover-from-file-system-corruption-using-fsck-and-a-recovery-iso
Thank you ! You saved me from the struggle of re-deploying a snapshot!
Start off by resetting your password. It should be emailed to you and then simply go into your profile and add another key. A couple of screenshots to get you on your way. I'd Google (or whichever search engine you prefer) how to do this though. You'll resolve your issue much sooner that way than waiting for someone to respond on such a question.
http://screenshots.wild-wild-web-projects.com/183gs/2yh8lFUO
http://screenshots.wild-wild-web-projects.com/SjdM/3cIrM0Fk