My router gets cut off when my flatmate tries to connect her laptop from her room. The router is set in the hall. Her room is further away from mine. There don't used to be a problem before. We don't know if it's her laptop or the router is causing the issue. I am using DSL connection and the WiFi router is Smart RD SR360n https://www.acanac.com/hardware/smart-rg-sr360n/?package=fibre given by our ISP. What should we do to troubleshoot this issue?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic