Q: Internet connection stopped working. How do I check the last time the ethernet port worked properly?

it shows under Active Services.  When I click on it, it shows a lot of information about the Built-In Ethernet.  Is there something in particular I am looking for?  Thanks.

If it helps... when I open Internet Connect, it does not show Ethernet any longer (it used to).  When I click on Airport - it says that Airport is connected to my network, and then it says 'Connected to Internet via Ethernet'.  But when I open System Preferences and click on Network - it brings up Airport (top in the list) as Green and says I am connected to the internet via Airport (which it is not).  Built In Ethernet is below (and shows yellow) and says it is currently active, has a self-assigned IP address, and may not be able to connect to the internet.

Okay - set up the new location, made certain Built In Ethernet was on top of the port configurations, and entered the DNS #'s indicated.  When Itried connecting to the internet, I'm getting the sae situation as with the 'automatic' location... the system tries them in order, and ultimately shows Airport as the one active and 'connecting' to the internet with Ethernet listed as active, but indicating it has a sef-assigned IP address and may not be able to connect to the internet.

On the Ethernet status screen, there is an IP address being assigned automatically with a subnet mask listed, but there is nothing listed for the router.  The airport status screen on the other hand, shows IP address, subnet mask, and router location.  It seems like the Ethernet simply cannot 'find' the router or vice versa.  Thsanks for your assistance.  I haven't tried your instructions for going back in time to see if I can find when the problem started.  I will do that later today.

Sorry - the 'back in time' were instructons i saw on another posting in help.  Not sure if that would help or not.  Cannot understand what would cause the ethernet port to stop working.  Any other 'logic' or files that may have gotten messed up?  How would I research this?

I am not aware of any spikes recently, but I could not say for certain if this happened ad has caused a problem.  Other than the ethernet connection - all else seems to be working fine.

I tried your suggestion above, but there is still no router showing under either Location for the ethernet.  There is an assigned IP address when I choose TCP/IP under the Ethernet connection.  If I select PPoE, then nothing shows up for an IP address.  Regardless, there is a problem betwenn the ethernet port and the router.

Is there any way to go back in time and discover when it ceased working?  Are there any settings or information under [Apple Icon at top left>About this Mac, then click on More Info, then click on Network] that would provide any guidance?

Any way to 'test' the port itself?  And if we are exhausting all options for getting this to work, any idea what is takes to replace the port?  Thank you!