Ok, friend, I'll help you solve it. You said you could surf the internet before, but now you can't. Is your local connection normal? If not, there is probably something wrong with the network cable. If it is normal, you can enter cmd enter in the start-run, and then ping 127.0.0. 1 to see if there is any data, indicating that the network card is good.

What I want to say is that your classmate blocked your network card address in the router, that is, there is an item on the router that restricts your address through MAC address filtering. Do you understand?

To prove this point is simple, you can unplug the network cable connected to your computer and connect it to your friend's computer. If he can surf the internet, haha, then I can be sure.

Extra points.