Hi people, French "user" here, try english as adviced. 

Context: Large two-story house. The Livebox and the RJ45 network patch panel are in the basement. The box's basic Wi-Fi signal is very weak, if not nonexistent, on the first floor.

Objective: To extend Wi-Fi coverage to the first and second floors. By connecting the first "satellite mesh" via RJ45 in a bedroom, and then the second via Wi-Fi on the second floor.

I launched the Deco app, and the first attempt to connect directly to the first floor failed. Second attempt in the basement, 20 cm from the Livebox. I managed to launch the app, configure the Deco access point, create a Wi-Fi network and password, and the app indicated that it was OK (even though the speed seemed extremely slow, 13/14 Kbps).

The Livebox configuration panel (198.162 etc.) recognizes the device as connected (I verified this on my main computer). So I decided to move this access point to the first floor where it should be. But... disaster struck! It can no longer connect via Ethernet and remains a silent red light despite restarting. It also disappears from the connected devices tab for port 4 on the Livebox.

I also tried switching the access point to Access Point mode. I read somewhere that the Livebox already acts as a router and that I needed to switch to Access Point mode. But it doesn't work for me. I'm really stuck. Could someone help me if they know about this type of problem and configuration? Do I need to set a static IP address? Configure something else? I'm completely lost, and I'm way too tech-savvy.

Here above is google translate... Anyway, I'm not sure that i must stay in Acces Point, someone on the livebox forums told me to go back in router configuration. Also i ask myself If static can be ok, but with all possibility (NAT/DHCP and so on) i'm clearly lost, as i don't really understand how it's working and how to choose wisely. 

Does anyone can help me? With maybe little knowledge of french Orange/livrebox Provider? 

Thx to you