what is happening with my internet

i have 2 routers. router A is in the living room and router B is in my bedroom. the main internet wire from our isp goes into router A and i extended a long network wire from router A to router B so i can have wifi in my room

there are times when the internet cuts in the whole house and an ! appears next to the wifi connection symbol and it's like that for all the devices at home which are in the living room and my bedroom. fixing that is easy. i just have to switch off router A then switch it back on and then the internet comes back in the whole house

there are also times when the internet only cuts in my room and an ! appears next to the wifi connection symbol only for the devices in my room. sometimes i can fix the issue by switching off router B and switching it back on and then the internet comes back. however, there are times when it's very stubborn and the internet wont come back regardless of how many times i switched off router B then switched it back on. the weird thing is if i connected the long network wire directly to my laptop then my laptop has internet

yesterday i wasn't able to bring back the internet when it spoilt only in my bedroom so i called the repair guy who extended the long network wire to my room. he asked to which port in router B is the long network wire plugged in. i said it's in the internet port. he said that's wrong and it should be in port number 4. i put the long network wire in port number 4 and the internet came back without me having to switch off router B then switch it back on

today the internet again only spoilt in my room and it was stubborn and the internet wont come back. this is what i did:-
1) i switched off router B then switched it back on. the internet didn't come back in my bedroom
2) i unplugged the long network wire from port number 4 and i plugged it back in. the internet didnt come back in my bedroom
3) i switched off router B then switched it back on. the internet came back in my bedroom

this is what i don't understand:-
1) should the long network wire which goes into router B go into the internet port or to port number 4? the repair guy said that putting it in the internet port of router B is wrong because the main internet wire is going into internet port of router A and my long network wire is connected to a numbered port in router A thus the wire should be connected to a numbered port on router B. it worked when the long network wire was in either port
2) why the internet only came back if i first unplugged the network wire then plugged it back in and then i switched off router and then i switched it back on? why the internet didnt come back when i tried other things?

Typically you don't want 2 routers plugged in at the same time, both providing a NAT connection. The Internet port on a router is designed to be the one coming from your ISP and will then do a NAT translation from your Internal IP address to your publicly routable internet address provided by your ISP.

So, ideally, from your cable modem you plug in the ethernet cable to your Internet port, and then any other switches or computers into one of the other ports. So, the cable coming from your router to your other router should in theory go into a port other than Internet as you don't want this router translating addresses again. You really just want connectivity to your OWN network on this router so that it acts as a wireless access point.

So, on your setup, check to see if you can just make router #2 a wireless access point, rather than providing router features.

For my setup at home, I use a Google Wi-Fi mesh setup. I have the 3 unit Google-Wifi setup. Here is how I am hooked up
Cable modem to internet port on google wifi router.
Cable from internal network side of google wifi router to 8 port 10/100/1000 switch in my family room.
Cable from 10/100/1000 switch in my family room to upstairs 8 port 10/100/1000 switch in my gaming room.
Cable from internal network side of google wifi puck to 8 port 10/100/1000 switch in gaming room.

So, it goes Cable Modem > Google Wifi #1 > 10/100/1000 Switch #1 > 10/100/1000 Switch #2 > Google Wifi #2

Therefore, my wireless network is the same anywhere in the house. I can have wireless devices talk to Google Wifi #1 or Google Wifi #2, traffic between my 2 Google Wi-Fi devices is over my cabled gigabit ethernet instead of wireless.

I have my third Google access point in my basement. It connects wirelessly to Google Wifi #1. So, any traffic from devices connected in my basement go wireless between Google Wifi #3 and Google Wifi #1.

I have 0 problems with this setup. It works fantastic and is super simple to setup.

i'm sorry. did you speak in english? i didn't understand anything of what you said

Sorry, I tried to explain it as simply as possible.

You really want 1 router (your main router) to actually be a router and route traffic. You really want your second router to be nothing more than an access point. This is essentially what a wireless mesh network is doing.

Maybe this page will help:
How to Connect Two Routers (with Pictures) - wikiHow

You have double NAT right now. What you should do is plug the ethernet cable from the first router to the second one's LAN port (NOT WAN). Then configure it as an access point. Make sure to disable DHCP in second router if not automatically.