What you described is how WR841N should work.
If the modem router is not using 192.168.0.1, WR841N's will be 192.168.0.1 as default settings.

Hi Vivian, that was I expected, but the question is that if I run the default settings the wired internet access doesn't work (for any device connected trough LAN router ports). Wireless, however, works properly. If I connect the router to the modem through LAN port instead of WAN port in this case wired connection works, but obviously it is not the best solution.

As I said, it should work as the modem is connected to WAN port..
So your router is not working normally. Sometimes, to configure a static IP on the PC may help to login its web interface and access internet by LAN cable.
If it won't work, hard reset it to factory defaults and check if you can login via cable connection.
If still no luck, go back to your vendor and confirm if it is still under warranty.
Out of curiosity, what's the normal working temperature and serial number of your device? I heard a similar issue several months ago.

I been doing a trial and error, but I don't succeed in having internet conection on devices connected to the router through LAN Ethernet ports. However, wifi works well
I don't know if the problem is that I have as a main modem/router one with already 4 Ethernet ports, i use one of them to connect to the router, and wifi, and I use it as a DHCP sever.
So I wonder if in this kind of network coniguration I need to fine tune the settings in a different way.

Just as additional info, for a better understanding, this odd configuration is due to that I have a room in another floor and I extended an RJ45 cable, from my modem, to get them connected. In this floor I intended to have several notebooks and tablets connected either wired or Wireless.

Finally I got it. But I had to connect the modem to the router through LAN port instead of WAN port, but unfortunately this solution leave only three LAN ports out of four, free for wire devices connection. I set the IP address of the router within the main network managed by the modem, and disabled DHCP of the router.