Is N2 set up to record failed logins in the errorlog? Are there any such messages in the errorlog?
By the way, I would not recommend installing SSMS on the database server itself. It uses resources that should be dedicated to the databases, it means you have to grant users permission to log on to the server interactively, and it uses up one of the two RDP connections to the server, which may be needed by someone doing proper admin work.
John