Ethernet Not Connected - Cable Unplugged

[GatorsUF]

Device: iMac 21.5-inch Mid 2010 | MacOS Sierra

So I am at a loss as to why my iMac suddenly decided to stop detecting the ethernet cable plugged into the port. I've run through most of the troubleshooting stuff I can find, most of which was related to an update to a much older version of MacOS/OSX. The information I've found doesn't seem to apply as I don't have the file, that was causing this issue in the past, on my machine.

I've tested the ethernet cable plugged into my iMac on another computer and it works fine.

 

[960design]

Lightning strike nearby lately?
Bent pin inside computer ethernet receptor?

 

[Bart Kela]

Well, the first thing to do would be to try a different cables. Cables go bad, just like any other piece of hardware.

Next would be to try a different port in the hub/router.

The third would be to try a different computer (or another wired Ethernet device like an Apple TV) and hook up to the hub/router.

With these three basic diagnostic steps, you should be able to determine whether it's a hardware or software issue and if it is hardware, where the problem is localized.

Good luck.

 

[Strelok]

A lightning storm killed 2 or 3 of the 4 ports on my old Wireless Router once, so it could be that.

 

[GatorsUF]

Thanks for the replies everyone, sorry I guess I forgot some of my diagnostic testing so far.

I completely replaced the modem/router from Comcast as I initially thought that was the issue. I checked the computer with a new wire from the router to the computer with no luck. The wire that is there was tested on my windows laptop and it works fine on my laptop.

 

[960design]

We recently had a lightning strike run up the cable, burn through the modem, burn through the ethernet cable and fry the ethernet chip inside the Airport Extreme. When I type 'burn' I mean, I was sitting right by it when the lightning hit the tower outside, lit up the offices as it flashed through the ceiling and caught the modem on fire and smoked the ethernet cable.

The mac mini that was attached survived the ethernet cable burn but the cart the equipment was sitting on shorted from the coax cable ( it was lightly resting on the cart edge ) and received a lightning burn scar along its side.

What I'm getting at is that the ethernet chip could be burned. I was receiving the exact same response from the mac mini while plugging in several different cables.

 

[GatorsUF]

I guess it could be a lightning strike, no obvious signs of that happening but I guess it's possible. Aside from burned up cables and smoke everywhere how else would I tell?

My hope is that it was something software related like this issue from earlier versions of Sierra.

 

[Fishrrman]

You might try one of the numerous USB-to-ethernet dongles that are available.
Low cost, and it -might- solve the problem (granted, you will lose one of the USB ports).

I've seen some USB/ethernet dongles that also are a small "hub" as well. They offer ethernet a 3 USB ports.

"When nothing else works, try a different approach that might..."

Here's something else you might try to diagnose the problem:
Install a "clean copy" of the OS on either a USB flashdrive or an external drive.
Then, boot the iMac from the external, get the OS setup (simple account, etc.).
Now connect the ethernet and see if the port becomes active.
WHY go through the trouble of doing this?
It could be something in your -software- that is blocking the connection, or causing the ethernet port to be "ignored" during bootup.
Booting and testing using a clean install from another drive may reveal that.

 

[GatorsUF]

Here's something else you might try to diagnose the problem:
Install a "clean copy" of the OS on either a USB flashdrive or an external drive.
Then, boot the iMac from the external, get the OS setup (simple account, etc.).
Now connect the ethernet and see if the port becomes active.
WHY go through the trouble of doing this?
It could be something in your -software- that is blocking the connection, or causing the ethernet port to be "ignored" during bootup.
Booting and testing using a clean install from another drive may reveal that.

Thanks I think I will try that.

 

[ApfelKuchen]

While booting to an external copy of MacOS would work, there's a simpler way to perform the same test:

Boot to Recovery - it's a separate installation of the OS that's already sitting on your internal drive. https://support.apple.com/HT201314

Be sure to turn off wifi (wifi icon in the Menu Bar). If you can connect to the web (Recovery > MacOS Utilities > Get Help Online), then you've isolated the issue to the OS. If it still doesn't work, it's hardware.

If ethernet does work in Recovery, then reboot. Next thing I'd try is to delete and re-add the Ethernet service:

System Preferences > Network. Select Ethernet, then click the delete button in the lower left. Afterwards, click the add button, select Ethernet from the drop-down list.