Really Bizarre network issue

It sound like you have pretty much exhausted the trial and error method of troubleshooting. However, ther is one more thing you don't mention that you might want to try.

Either try the "problem" computer at the "problem" desk with a different patch cord or take the "problem" computer / patch cord combo to a different desk and try them there. I have seen in the past where a given path cord would no longer work with a certain computer (for no known reason). The problem cord would work withother computers and a new cord would work with the problem computer.

If this doesn't fix the problem, I would hazard a guess that you have seriously displeased the IT gods and they have retaliated by visiting upon you a plague of gremlins. You may need to pause for some serious self-reflection to discover how you displeased them and how you can regain their favor.

Good Luck.

sounds like a physical problem. Some male and female plugs just do not like each other- but will work fine with every other. Try playing with the connection pins. If this one machine works everywhere else then thats it. Why not put it somewhere else? Does it have to be there?

After replacing the jack to nic cable, if it still does not work, problem could be;

1. bad connection in the jack

2. bad connection in server room

3. bad patch cable in server room

4. bad connection/termination on the cable between the server room and jack.

5. RJ48 jack or NIC's connector is dirty/oxidized.

The above could cause the transmit/receive to be below the operating parameters for the NIC on this particular computer, so you would not be able to "SEE" the network.

Have you tried plugging the 3com NIC into the other computer and test? It should be the female jack of the LAN card got some bad contact with the suspected RJ45 jack. Try to make a new patch cable or swap the NIC.
GOOD luck! :-)

Oops. Left out some details. I tried two different NIC's (same brand/model, but different cards) and three different patch cables, all with same result. I suppose it is possible that the 3Com 3c905btx NIC in general has a problem, but that seems unlikely. That's the card we use in 75% of the computers in the firm, and have never had a problem.

Hi,

My guess is that you actually have two problems. Firstly the cable between the wall and the patch panel is likely damaged - maybe it has been bent too much...

And secondly, either the brand of NIC you're using is more susceptible to low quality connections than your hub - it just happens that both examples you tried wouldn't work in that PC or - there is a subtle problem in the PC itself making the NIC overly sensitive.

Cheers,
Tim.

I would check the wiring of the cat 5 run on both sides. If you have a cat 5 tester it would be even better. It looks to me like you may have a wire crossed.

I once had the same problem and found that when I disconnected the cable from the patch panel and reconnected it it then worked without a problem. Apparently it hadn't been tight in the panel and this one computer was just more finicky than the others.

You didn't mention how many hubs/switches were involved. Try manually setting the NIC to 10mb/sec half duplex. Many NIC's are not good at auto-sensing. I've seen it many times on Dells. In addition, if by chance the wiring between that office and the wiring closet is mechanically sound, but impropery mapped it may work with some NIC's and not others. I've seen many NIC's that simply won't work, at all, at 100mb/sec if the wiring isn't to spec.

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