WLAN throws out my roommate?

As soon as I log in to the WLAN with my Microsoft Surface, at least the WLAN will no longer work on a laptop of my roommates. What can I do?

Check with you as well as with the laptop whether there's a fixed IP address set.

How do I look it up?

Does it work if one of the devices or both is connected by cable (with WLAN disabled)?

Where you look up the IP addresses:

Somewhere in the internet settings. For Windows:

https://www.google.com/...irloom-srp.

That's the most likely cause.

It is best to set both devices to "automatic".

If that does not help (or both already stand on automatic):

Extremely unlikely, but not impossible: Conflict of the same MAC addresses - see https://www.google.com/...-srp.2.0l5

if both MAC addresses of the WLAN "devices" should be the same, it is essential to change at least one of them

If that does not help: look in the settings of the router, which addresses are not automatically assigned and give both devices different (!) Fixed IP addresses (preferably from the three-digit range 100 to 254), otherwise from the two-digit range