Presumably only one of the NICs is connected to a network which has Internet access?
The GUI way is to go into TCP/IPv4 Properties, Advanced, and set a default gateway with a metric lower than any other default gateways (Windows will prefer the default gateway with the lowest metric). If you're still a bit stuck, do a "route print" and show us/me - via Hangouts if you want it less public.
If your machine is configured to use a DNS server on one of the local LANs, you'll need to make sure it's reachable.[...Insert Brain Here...] |