...but it will work through a USB port (with an adapter) for a while.
However, this too will quit in a few days.

Have done the full Diagnostic analysis on the Dell support site. The results are simply that the cable is unplugged - wrong!

So it looks like the physical port. Can this be repaired?


I know I can just add another card - but I'd rather fix it to avoid a "contagion of electrical failure". The audio port right next to it suffered through an issue with a 'ground connect loop' which seems to have blown the speakers and I'm worried this was somehow involved.

I assume you have checked the obvious, physical connections LEDs illuminated on both end of the cable, ethtool showing a good link status? etc.
Its possible you could have a driver issue but with two different adapters its a long shot.

If the USB adapter also quits withing a few days then it could be whatever is down stream is also bad or a combination of problems. Can you or have you switched ports to see if that makes a difference?

A ground loop that caused the speakers to blow might of caused other damage to the motherboard. You might have a PSU problem with some of the output power connections.

Did it ever work?

Make a loopback connector maybe and look for blinky lights.

Results of lspci?

Uhhhhh?
Having the physical ethernet port on the machine quit then also a USB adapter ethernet quit points to the possibility of a problem outside the machine.... i.e. the router or switch.

It is also possible, since you also have an audio port issue, that the board may be damaged so symptoms are seen in several places. Ethernet, audio, USB, etc.

If the physical ethernet port on the board is failing or some component has become temperature sensitive, then a new motherboard will be the least expensive and most reliable fix, even if it is otherwise repairable.