>In 22+ years of computer support, I've seen a network cable "go bad" exactly once. I suspect, in that case, it was a marginal cable to begin with, and one of its connections degraded to the point where the cable didn't work at all any further.

Thanks a lot, this is a very detailed list of things to watch for. I will forward that to the network specialist, just to make sure, at least, all those points would be covered. We never know, maybe one of them was not checked.