Enable addtional NIC?

This might be an easy one for most of you, but I just cant swtich my additional network card on.

I am trying to enable 2 network cards on the same computer ( they are not identical), but seems like i can only use 1 network card at a time.....this is what i am trying to do.

Router -> main computer -> computer2

I have 2 network cards on main computer, one from router in, the other is for computer2. Cant get the one from main computer -> computer2 "ON".

I guess it will be easier if i just get a really long cable connect from router straight to computer2 but...no

Any advice or comments will be nice. Thanks

something wrong with your pc? get a new one then!