Jarsky, thanks for the reply.... IF your issue is similar, then switching hardware, like your new router, or even getting lucky during one of the driver reinstallations can fix the issue... unfortunately, it may happen again within a few weeks.... it seems that whatever conflict is causing this does not happen each time you boot or run the computer. Many times I have been relieved to fix my internet connection, only for the problem to come back a few days later.
Also, the newer nvidia gig-ethernet port, when it is working, works perfectly fine in 100MB mode, or 10 MB, half duplex, full duplex... In fact, the date that I got my motherboard I don't think any company was making n routers yet, and most people were hesitant to get them if they did come out since it was still a 'draft'. If it was having issues with an older router, I am *fairly* certain that you would have an error relating to tcp/ip or ip address resolution.... basically your network icon would have that little yellow !, instead of the red X saying 'network cable unplugged'. If you were to plug the cat5 cable into almost anything (a switch connected to nothing, the back of an Xbox 360, a cable box - basically anything that would not provide the correct information or even attempt to) with a power source, usually the device doesn't even have to be turned on, the "unplugged" message will almost always go away and you will get an error instead.
The onboard nvidia network controller has **successfully** connected (wired) to all of the following for at least some period of time, long enough to access the internet: non-wireless linksys router, linksys G router, linksys N wrt150n router, belkin wireless N router w/ network storage, and a netgear G access point WPN180N ...
the problem isn't in the drivers, the cord, the external hardware, etc... And when searching the internet for nVidia nforce "network cable unplugged" I find many posts where people are told to go through almost all trouble shooting scenarios and nothing works.... and in some they report back that after uninstalling and restarting the machine so many times, it finally started working again (as if some sort of luck is involved, perhaps the computer finally providing PCI bus/IRQ/memory resource information that is no longer conflicting while the driver is installed)
In my bios there is a place to set the COM location... Although I have tried changing this to fix the problem without success...
It leads me to believe that a possibility for the reason it also occurs with a PCI card as well may be the fact that I disable the onboard adapter when I use it, and because the computer recognizes it as the same type of device (wired network adapter), it uses the similar resources/IRQ or something of the sort, which allows the problem to occur again. However, my wireless N pci card had never had an issue.... ?
I think I need to learn more about IRQ and Com location settings so I can set it manually PRIOR to installing the drivers for the device, rather than after the problem has happened.
Anyways... I *DO* hope that your problem is fixed ;-) but even if your router was having problems with the network controller, I still think you would get something other than 'network cable unplugged'.... so don't be TOO surprised if that little message pops up yet again.