Ethernet limited connectivity?

I have two computers, both with 32-bit Vista SP2. At my old house, both connected to the internet just fine through an ethernet router. At the new place, computer A connects through the same router (different modem, different ISP) as before just fine while computer B says it has limited or no connectivity. The problem isn't the router or the ethernet cables. It has an nVidia nForce 10/100.