If you have accidentally connected an analog phone line to the network connector, the 48V idle voltage may have damaged the line interface IC. This will not necessarily be detected by the OS if the rest of the network controller circuit is still working. But the keyboard problem indicate that something else may be wrong. Anyway, a soldering iron and/or a sledge hammer may be necessary.

>Yes, it does seem to be more like a hardware problem that software.
>
>>The missing LED flashing when you plug in the cable is a pretty clear indication of a hardware problem inside the computer.
>>
>>>I disabled the fire wall but that makes no difference. I have not instituted mac filtering; where do I find out if it is?
>>>No zones or domain changes. Computer name has not changed and not other things that you listed.
>>>And I did try different ports on the router but still, no connection. And I know it is not a physical connection from the cable into the computer since I tried plugging the cable into the computer and into the docking station; either way it does not work. Something " inside" obviously has changed but what... Anyway, thank you for the input.
>>>
>>>>Any new blocked zones in your firewall? Or has the mac address changed since you instituted mac filtering? Is there any filtering at all right now? Any zones? Any domain changes? Any computer name changes? Any gateway or dns changes? Does it work with the firewall shutdown? Anything in the hosts file? Just a bunch of stuff to rule out.... Does a different port on the router/switch work?
>>>>
>>>>Does your wired connection work anyplace else?
>>>>
>>>>>Hi,
>>>>>
>>>>>I was using my PC earlier today on a wireless network (at home) without any problems. I came in the office and plug in my cat5 cable but the network icon says unplugged. I tested the network cable on another computer in the office (on which I am typing now) and it works. But when I plug it into my " other" pc it does not work. In the Control Panel -> Networking, the network card does not seem to have any problems. That is, it says, "working properly"
>>>>>
>>>>>What else can I do to troubleshoot this issue? Maybe related or maybe unrelated, also this morning the cordless keyboard does not communicate with the computer.
>>>>>
>>>>>TIA for any suggestions.