@ukanonymousuk I've tried a wired LAN connection for the laptop, but the result is the same—all other devices lose internet access as soon as the laptop is active.

ukanonymousuk wrote

  @ukanonymousuk I've tried a wired LAN connection for the laptop, but the result is the same—all other devices lose internet access as soon as the laptop is active.

  @ukanonymousuk 

Hi,

But with the original Wi-Fi card installed in the laptop this did not happen?

Is there any chance the laptop may be running software that utilizes a technique called "ARP spoofing"?
 

  @woozle I haven't checked it with the old card; I got the router and the card on the same day and set everything up at once. I'll check for ARP, thanks.