Disconnected : No supported authentication methods available (server sent :publickey)

For the record, the usual default username in EC2 for these Linux distro:

• Amazon Linux: ec2-user
• Ubuntu: ubuntu
• Debian : admin

To access the instance through a browser, make sure you add a rule in your security group to allow port 80 and port 443 inbound.

I was having the exact same problem on Amazon EC2 and I simply changed my username to "ubuntu" and it made a connection.

Use the public dns name instead of IP. In the putty, choose connection > SSH > Auth. You will see the Authentication Parameter part, in there you can choose your ppk file.

And one more very important thing. Click the "Allow attempted changes of username in SSH-2" to activate it.