If this is a home computer you go into your router through your browser usually by default you can type in 192.168.0.1 and it will take you there. Once there set up a user name and password. Then in your pc you'll have to pute in the same name and password just check the remember box and you wont have to every time you log in.
Apart from making a password for the router, what are you talking about?
Also block the IP from you router.
If he would be hacked if he doesnt block this ip, blocking a single ip would make no sense because EVERY ip could be malicious for this router then.