Wi-fi working perfectly, Ethernet connected but no internet access

Strange scenario with a Macbook Pro. When the ethernet cable is connected the internet connection is dropped, despite the fact that it is properly connected via air port. The ethernet connection is detected and displays CONNECTED. When I connect the same cable to either my G5 or other Macbook, there is no problem.When the ethernet cable is disconnected there is no problem connecting via air port. Turning off airport when the cable is connected (and detected) makes no difference.
The network configuration in both laptops is the same: DHCP is enabled, IP addresses are correct and the router that the cable is connected to is detected. The only strange issue is that on the Macbook Pro with the ethernet connection scenario, only one DNS server is displayed and on the other Macbook (with no problem) there are 2 DNS servers displayed.

Problem solved. Just needed to manually add the DNS address on the Macbook with the ethernet connection problem to match the other laptop. DUH