You would be surprised how many brute force attempts you can log just by turning on an FTP or SSH service for a day. There are billions of zombie computers that spend all their scripted lives scanning IP ranges and when they find something interesting, the try to log in. The humorous part is how many of these will try to log into *nix SSH using the username Administrator, Admin, God, Mary, etc.
If you do not have any services running, the best thing to do would be to block/drop incoming connections that are not part of already established sessions (ie: requested connections, as in a webpage you want to view). Most standard firewalls have this capability, although the language used to describe it will vary.