Zend certified PHP/Magento developer

Putty; Server refused our key

I am trying to start up my first ever PARSE server but I can’t get it started. When I try to access the instance through PuTTY it keeps bringing up the error putty fatal error no supported authentication methods available (server sent publickey). It says the server has refused the key. I have followed the instructions given on the aws.amazon site and have gone through the troubleshooters too. Any advice appreciated.
I think the Host name is wrong, AWS has told me to use ec2-user@ and then use public dns name but I think that might be wrong