On a 2.16 GHz Intel core 2 duo, running OS 10.5.6 with 2 GB RAM, model "imac 5,1"
This is one of 10 identical machines in a university lab. No updates or changes of any kind have been implemented. One day, it stops accessing the Ethernet network. The Network preferences say "cable not plugged in" when it clearly is.
I did a restart, zapped PRAM, unplugged it and reset the whatever it is that resets, ran permission repairs, all to no avail.
When I swap cables with the machine next to it, the problem stays with this particular computer. In other words, the cable and the network port are not the problem.
I hauled it down to the nearest Genius Bar where, of course, the Ethernet mounted instantly. I took it home, plugged it into my cable modem, and still got the "cable is unplugged" message. This despite the fact that my home iMac is using that same cable for internet.
Brought it back to the lab, and tried plugging it into 3 different ports, using 3 different cables. "Cable is unplugged."
A Google search on the topic shows a fair number of people with the same problem, but no solutions. And I am worried because a 2nd computer started displaying the same symptoms. That one responded to my basic ministrations, but I'm concerned that this is an impending problem for all 10 of these machines.
What can I try?
Various and sundry, Mac OS X (10.5.5), Run a lab, got a lot.