Why does the DIR-300NRU router not see the network cable?

Question

network hardware

I've encountered behavior I've never seen before.
The provider Triolan (Kharkiv) gives the Internet to the apartment, and the cable is quite long, 15 meters (some people think that this may matter).
Previously, the Internet came to some kind of switch, a DIR-300NRU was connected to it, which successfully distributed the Internet.
The configuration has changed. The switch had to be removed, and the network cable plugged directly into the router. At the same time, it turned out that the WAN indicator (planet) does not light up and the provider, accordingly, does not see the router in its network. After several experiments, I found out that when the router is turned on, the link rises for some seconds, the indicator lights up, the provider manages to see the router, but then everything falls down.
I decided to find out everything is fine with the router in the hardware sense. I go to the next apartment, where the wire from the same provider comes in - the router sees it perfectly and the link rises.
I take the problem cable, insert it into the laptop - one, the other - the connection is normal, the Internet is working.
I'm surprised.
I insert the problem cable into another router - TP Link - everything is fine with it.
So I concluded that physically everything is fine with the router, but for what reason it does not see a specific network cable, I did not understand.
Downloaded the latest firmware, updated
DIR-300NRU rev.B5/B6
Firmware version:2.5.11
Build time:Mon Jun 8 16:32:18 MSK 2015
Description: Root filesystem image for DIR-300NRU rev.B5/B6
As a result, the behavior has not changed, the link does not see. I had to be smart: I plugged the network cable into a working router, I already threw a problematic router to it (WAN caught fire!) And that’s how I set up the Internet. Unfortunately, the working router will have to be given away soon, so I would be grateful for advice on what could be in the DIR-300.

Answer 1

0) Re-crimp (replace) the connector on the wire. Did not help?
1. To control, poke the provider's wire into the LAN holes of your router.
a) Do the lights come on? The problem is in the router, try to change it under warranty.
b) Do not light up? Call the installer from the provider, let them figure it out.
2. No warranty? find / buy a switch, as it was - it will act as an amplifier. Or buy another router.

Answer 2

Re-crimp the cable.
It happens.

Answer 3

You can check the link on the cable using lan ports, if there is no link, then either all ports are burned out, or the cable is damaged, or the provider has a jamb on the equipment