Do you have any firewall software or antivirus on your computer?

You have to change LAN IP address for another subnet, for example 192.168.1.1

So, I thought that only opening the port on the router, I would see that is opened in a web site like the one I showed in the first message. This port is open because tester can see your router (web...

Do you have any service on 53 port now on your computer? This is very important to listen on this port.

I have to unplug it and replug it in. Do you say about RJ45 plug i WAN port?

First, change the password for the router because you have default configuration admin/admin :) Have you tried with DMZ settings? Port 53 is typical DNS service.