How to make a computer so it's no longer able to acess the internet?

[Richard]

Yes and its quite simple to do uninstall your network drivers. In control panel go to hardware and sound under devices and printers click "Device Manager", a window will open up with a list of all the drivers and devices; look for Network Adaptors and click on it. You should see something like Ethernet Controller and if you have a wireless card there will also be something Wireless Lan. Back Click on both and uninstall.

Warning though after doing that and rebooting you will get a lot of error popup's for things trying to connect to the internet.