So which NIC is not being activated, internal or external?
What type of broadband service do you have, DSL, cable etc...?
Do you have a dynamic or static external IP address?
Post the contents of /etc/modules.conf file
Does it show an alias for eth0 and eth1?
Does the output of ifconfig show something for both eth0 and eth1? Try manually configuring an IP address.
ifconfig eth0 192.168.0.1 netmask 255.255.255.0 up
Replace eth0 with eth1 if that is the misbehaving interface.