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Networking Questions and Answers - Ethernet Port Says Cable Not Plugged In
Bryan writes in with a networking question
Question:I have seen a few laptops with this issue. Even if there is no Ethernet cable plugged into the port the link light will still be on. I have checked when you do plug a cable in and it keeps saying no cable is plugged in. I have tested the Ethernet jack and the cable on a different computer and it works. So I know it has to be a problem with the Ethernet port on the computer. I am wondering, can a virus cause this to happen? One of the computers I was messing with I managed to get a brief glimpse of hope as I saw the link light flash then just stay on and not move. After that I opened up the command prompt and checked the IP and I was getting a 169 IP so I tried to do the netsh winsock reset then restart the computer and after I did that I was not able to get anything at all. On that computer it was loaded up with all kinds of file sharing programs, so that made me think that it could be a virus messing with the port.
Answer: It's unlikely that a virus is affecting the physical port itself but may be doing something to block access to the port. Since you are getting an APIPA IP address (169) then your computer is not able to talk to your DHCP device. I would boot into Safe Mode with networking and see if you can get a connection/IP address that way since many virus and spyware programs don't start up in Safe Mode.
If you know the IP address and subnet mask of your network or if you have another computer connected to check the settings then you can assign a static IP address and see if you can communicate that way.
You can also go into Device Manager and remove the network card, reboot and have Windows find it and reinstall it to see if that helps. Finding and installing a new driver may be helpful as well.
Another way to check the port is to check the link light on the other end of the connection. If a connection is being made and packets are being send then you should get the link lights on the other end of the connection such as your router or switch to light up even if your computer doesn't have an IP address. If the link light on the other end is not lighting up then you may have a faulty Ethernet card itself.
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