Device Info of course.

Hi, I'm Martin from Poland :) We are very happy that you are very glad from this forum. We try make good job and help all.

No, I have asked about DHCP Settings, maybe give me STATUS tab from your router too.

I thought that the signal would get much bigger If it's possible you have to lay cable from main router to another room and there connect tp-link.You'll have strong signal in another localisation.

Give us screenshot from DHCP, you can try connection without security settings.

Make cable connection between routers. You can use WAN port in WR841ND configured like Dynamic IP.