Ethernet not working: how to fix it

Acutis · plain-English network help · updated June 2026

You plugged in a cable expecting a fast, stable link and got nothing, or worse, a connection slower than the Wi-Fi you were trying to escape. Wired networking has fewer moving parts than Wi-Fi, which is good news: there are only a handful of things to check, and you can isolate the fault quickly.

Ethernet not working: start at the physical layer

When Ethernet is not working at all, the first suspects are the cable and the port. Before touching any settings:

• Look at the port lights. Most Ethernet ports have a small LED that lights or blinks when a link is established. No light usually means no physical link: bad cable, bad port, or the other end is off.
• Reseat both ends. Unplug and firmly re-click the cable into the computer and the router or switch. Listen for the click.
• Swap the cable. Cables fail silently, especially where they bend at the connector. Try a known-good cable.
• Try a different port on the router or switch. Individual ports do die.

If a different cable in a different port lights up and works, you have found a dead cable or a dead port and you are done.

Check that the operating system sees the connection

If the link light is on but you still have no internet, check what the computer thinks is happening.

Windows: open Command Prompt and run ipconfig /all. Look for your Ethernet adapter. If it shows an IP address starting with 169.254, the adapter never got an address from the router (a DHCP failure). If it shows "Media disconnected," the OS sees no link at all.

macOS: open Terminal and run ifconfig en0 (the wired adapter is often en0 or en1). An inet line with a real address means it connected.

A quick reset of the address often helps: on Windows run ipconfig /release then ipconfig /renew.

The driver

If the hardware looks fine but Windows shows the adapter with a warning, the network driver may be missing or corrupt. Open Device Manager, expand Network adapters, and look for your Ethernet controller. A yellow triangle means a driver problem. Right-click and choose Update driver, or uninstall it and reboot so Windows reinstalls it. After a major OS update, reinstalling the manufacturer's driver from their site sometimes restores a port that quietly stopped working.

Ethernet slower than Wi-Fi: the duplex and speed mismatch

If Ethernet connects but is bizarrely slow, the usual culprit is a link speed or duplex mismatch. A gigabit port that negotiates down to 100 Mbps, or worse to "half duplex," will crawl.

• Check the negotiated speed. On Windows, in the adapter's Status window, look at the Speed field. If it says 100 Mbps on gigabit gear, something forced it down.
• The cable is the most common cause. A damaged cable, or an old Cat 5 cable, can limit you to 100 Mbps. Use a Cat 5e or Cat 6 cable for gigabit.
• Leave duplex on auto. In the adapter's Advanced settings there is a "Speed & Duplex" option. It should be set to Auto Negotiation. A hard-coded setting that disagrees with the switch causes a duplex mismatch and terrible throughput.

Is the NIC dead?

If the same cable and port work fine for another device but never for this computer, the network card (NIC) in this machine may have failed. Confirm it:

1. Plug a laptop you know works into the same cable and port. If it connects, the wiring is fine.
2. Back on the problem machine, if no cable, no port, and a driver reinstall change anything, the onboard NIC is the likely failure.

A dead onboard NIC is not the end. A USB-to-Ethernet adapter or a PCIe network card is a cheap, reliable replacement.

A clean order to test in

1. Link light on? If not, swap cable and port.
2. Does the OS show an IP? If it shows 169.254, release and renew.
3. Driver healthy in Device Manager? Reinstall if not.
4. Connected but slow? Check negotiated speed and cable category, leave duplex on auto.
5. Works for other devices but not this one? Suspect the NIC.