I have the following and i need to clone the repository in either windows terminal command prompt or linux.
in the command line run ssh -T git@github.com
(see https://help.github.com/articles/testing-your-ssh-connection/)
if that works, bother with git next. but likely there will, be your issue.
to clone, THEN use git clone git@github.com:$USERNAME/$REPONAME.git