Run these commands on putty:
yum groupinstall 'GNOME Desktop Environment' 'X Window System'
yum install nx freenx
shutdown -r now
Download the software from here: http://www.nomachine.com/download-client-windows.php
While installing, use Gnome interface.
Get the key by running this command via SSH:
Copy the resulting dsa key with Control + C .
The login credentials would be root and your root password.
You may also refer to this article: