@Shafiul_1112 

If you bring laptop to Main Deco and connect laptop with Ethernet cable to the second port of Main Deco, will laptop connect via Ethernet?

  @Alexandre. No!

  @Wrayman Yes, it sounds dumb. I really feel dumb buying this product :(

1. I tried changing ports and the devices. I have 3 devices. So I tried all ports but the PC/laptop doesn't connect

2. I don't have IPTV, yet, I tried your option. Same result!

3. My PC doesn't even have a WiFi device! So, no option of that. Anyway, I tried with Laptop, but same result!

Now I'm stuck with: the original modem from the operator, 3 deco and one old WiFi router to connect my PC & TV to internet.

I really feel dumb buying Deco E4

Shafiul_1112 wrote

  @Alexandre. No!

  @Shafiul_1112 

Main Deco plays the role of standard WiFi router. Its second Ethernet port is LAN port.

By connecting PC/laptop to Main Deco with Ethernet cable, you changed problem from "can't hardwire to Deco mesh" to more generic "PC can't connect to LAN."

I recommend googling for "pc cannot connect to lan network" and follow recommendations, which are many. 

  @Alexandre. I think I couldn't make it clear to you.

I didn't try the main deco first. I tried connecting my PC with a satellite deco first! And yes, I tried the second ethernet port (LAN port). When it didn't work, I tried with another satellite. It didn't work.

Then I tried connecting in the first port of one satellite deco. Then the other satellite.

Then I tried connecting my old WiFi Router with the satellite and the PC with the wifi router. It worked.

Then I tried connecting my PC to the second port of the main deco. It didn't work.

Only after trying these, I switched the first port on the main deco.

Then, I reset the full system, and repeated everything I already did.

  @Shafiul_1112 

It may be as simple as having static IP address configured on PC. Deco mesh could provide IP addresses in different range than your previous router, that would prevent device with (now incorrect) static IP address from connecting to the Internet.

Think about Deco mesh as WiFi router. Your problem is you have PC that can connect to LAN of old WiFi router, but not to LAN of your new WiFi router. If you think about it that way, you may be able to fix it, because you will focus on PC networking settings.

If you think of it as "TP-Link Deco problem" and expect fix by changing settings in Deco app, you won't have a fix.

In situation like yours I would:

1. Check if PC is configured with static IP and change in to dynamic;

2. Do Network Reset (under System/Network&Internet/Advanced Network Settings);

3. Run "Find and fix Network Problems" troubleshooter you can find under Settings (just type it in Search window of Settings).

If that does not help, I would start googling for the phrase I provided to you in my previous reply.