Glad you got it worked out in the end. I can't believe that in 2014 an operating system still can't set up a NIC properly. So far I've tried a board with dual NICs, both realtek. Both had the same issue. Now I'm using a different motherboard with a single Intel NIC (82579V) and it's still happening.

I've installed all available updates, updated the kernel to the latest available, and installed the latest Intel drivers from sourceforge. Rebooted countless times. I don;t know what to try next.. Whenever it messes up it can be fixed by simply clicking the network icon at the top right of the screen and clicking on "Wired connection 1".