First, go to terminal and run ifconfig and paste the output back here. That should help us get a better understanding of where the problem is.
Have you tried disconnecting from the wireless network? If not do so and then try connecting via ethernet.
Have you tried adding a new interface for your ethernet adapter using the GUI? If I remember correctly it should be under System-->Network Connections or something similar. I have no idea why but in the past I've added a new instance to the list with the exact configuration of the one that wasn't working and had no problems afterwards
Anyway, make sure you're connecting automatically, be sure DHCP is on if you're using that, and let us know how that works out.
