That bit about the port light flickering like a candle in wind is exactly the kind of thing that makes you feel dumb after the fact. Had a buddy hit almost the same wall last year, workstation kept dropping every half hour, and he's in there swapping out the card, updating drivers, the whole nine yards for most of an afternoon. Turned out the cleaning crew had bumped the desk and the cable was hanging by a thread at the wall jack, barely making contact. He finally noticed it when he leaned on the desk and the link light blinked out right in front of him. He was so mad at himself he didn't even bill the full time. Swear that stuff humbles you faster than any weird software bug ever will. Physical layer first, every single time, and I still catch myself skipping it when I'm in a hurry.