Ran into this problem myself, but the "unplugged" message would alternate with the exclamation point error saying there was "Limited or no connectivity"
Maybe my solution can help others:
Boot into Safe Mode with Networking (press f8 key after reboot and select "Safe Mode with Networking" from the menu that results)
Does it work there?
If so, go to START > Run
Enter "msconfig"
Click "Services" tab.
Check off the "Hide all Microsoft Services" check box to check it off.
Disable all the non-MS services and reboot into Normal boot mode to see if the networking issue goes away
If it does, re-enable the services a few at a time until you find the culprit and either leave it disabled or find a fix if one is available (an update or patch?)
In my case, "Broadcom ASF IP Monitor" service was killing the Broadcom 57xx Integrated Gigabit Ethernet on the desktop I was working on.
The OP is likely long gone, but I ran into this in 2012, so necroposting might be forgiven? I Googled this pretty thoroughly and no one mentioned rogue services that can mimic a bad cable/hardware.