Router Disconnects from the Internet only when a certain PC connects!

I know that propably it's not a Windows 10 related topic but I didn't know where else to ask that.
I searched a bit on the Internet for a solution and I couldn't find any.

So whenever my brother opens his laptop and connects to the Wifi every other PC loses connection.
Router generaly is starting to act weirdly, random disconnects, connecting again for little, then again disconnecting etc etc...

Does anyone know what could be the problem and if you have something to suggest?

I don't feel like posting any info of the laptops we have here since i believe it's quite irrelavant to the problem.
The problem is what can my brother's laptop do in order to effect so much the Internet connection.
Yes i close all his downloading actions or programs that use Internet and still problem occurs.

Here in my house every one is completely clueless about technology and they think that ''just the Internet is bad and his PC doesn't affect it at all''...
So I am kinda the only hope to fix this.

Did your brother recently upgrade to windows 10?
This happened to a customer of mine just after upgrading. Every device would disconnect from Wifi when the PC was connected. No devices could connect either. After disabling the PC's network-adapter, the devices could connect immediately. Unfortunately, I had not much time to investigate (customer needed the PC). However, a clean install solved the problem.

Could it be related to this problem?
https://www.tenforums.com/network-sharing/13464-one-windows-account-causes-router-wi-fi-turn-off.html

Perhaps it's dhcp starvation. Worth investigating.

martins said:

Did your brother recently upgrade to windows 10?
This happened to a customer of mine just after upgrading. Every device would disconnect from Wifi when the PC was connected. No devices could connect either. After disabling the PC's network-adapter, the devices could connect immediately. Unfortunately, I had not much time to investigate (customer needed the PC). However, a clean install solved the problem.

Could it be related to this problem?
https://www.tenforums.com/network-sharing/13464-one-windows-account-causes-router-wi-fi-turn-off.html

Perhaps it's dhcp starvation. Worth investigating.

Thanks for the extra info and the reply.
I will look it up.