The network cord is connected, there is an Internet in the router, there is no network in the network connection, how so?

Question

Windows

There is a router to which several computers are connected through a switch. With wires everything is OK - 100%. On all computers except one with an Internet and a network, everything is OK. Only one computer says that there is no cable in it, but there is a cable in it. Moreover, a second network card was inserted, which reacts in exactly the same way - the wire is inserted, there is no reaction. Ports on the switch are OK (I poked the cord into other ports and the same thing). Before that, everything worked like clockwork. No prog has been installed before. Avast worked, it was demolished and there was no result (I read that there are problems because of it). There is a suspicion that this is a hardware problem, but there is not enough knowledge to test the hypothesis. On the switch, the light blinks periodically every 2 seconds.
What are your thoughts dear?