How to troubleshoot a dead port
Symptom: You do not have internet service, and when you look at your router the Internet/WAN light is off. You check the modem and its ethernet light is also off. All other light on both devices are on normally.
Troubleshooting: First you will need to preform what is called a loopback test. To do this, disconnect the ethernet cable from the modem and connect it to one of the LAN ports on the router. This means both ends of the cable will be connected to the router. This is called a loopback. Next check the router’s WAN and corresponding LAN lights. If they are lit then we can assume the cable and router are working fine and the issue is the modem. You can confirm by unplugging the Ethernet from the router’s WAN and connecting it to the modem. If the corresponding LAN light goes off this will prove the modem has gone bad. Alternatively if the lights to not go one during the loopback test, still preform the LAN to modem test and see if the lights go on. If so then the issue is the router’s WAN port. If not get a new Ethernet cable and repeat the test. This will ensure the issue is not the cable itself.
How to resolve: When a port is bad the only way to resolve the issue is to replace the equipment. If your modem is bad and you rent it from your ISP, just call your ISP helpdesk to get it replaced. If your modem is not rented or the issue is the router, then contact the device manufacture to report the issue and determine warranty eligibility.
TP-Link Support can be reached here: https://www.tp-link.com/us/support/contact-technical-support