How do I block a specific computer from my wireless router?

I live in an apartment complex and I have password security on the wifi already, but one of my roommates keeps giving the password to a neighbor girl he's desperately trying to get with and tells her the password every time I change it. How do I block her computer from router access even if she has the password? Is it possible to do without direct access to the computer?How do I block a specific computer from my wireless router?
You could do this by MAC filtering in your wireless router. Every wireless adapter has a MAC code - you can find out your own by opening a command prompt (run CMD) and in the command window, type ipconfig /all and hit enter.



Look for the MAC code (will be called physical address and will be 6 pairs of characters) of your wireless adapter and write it down. In your router settings enable MAC filtering and add your MAC code - set it to enable/allow if that is in the settings. Repeat for each laptop you want to allow and save settings if necessary.



Now no other laptop with an unknown MAC code can access your network as it restricts to only the ones you have entered. Of course if your roommate finds out her MAC code and adds it into the router himself you'll be back to square 1...How do I block a specific computer from my wireless router?
Whitelist only your MAC addresses so no one else can access it.