Having Problems Getting My Computer to Connect to the Router.

Hello everyone. Recently I just upgraded my old Windows XP to a Vista. I have
3 computers in all: 2 laptops (both run XP) and 1 desktop (Vista). My ISP is
cox Cable ad I use the Motorola Surfboard Modem and a Belkin Router. Back
when I had the windows XP desktop, I could connect all 3 computers to the
internet via the modem and router. But now I'm having trouble trying to get
the vista to connect to the internet. The internet works perfectly whenever I
connect the modem and the computer directly, but whenever I Connect the modem
to the router to the computer to try to get all 3 comps running the internet,
the desktop says it has limited or no connectivity to the network, but the 2
laptops can connect just fine. Ive tried calling both Cox and Belkin, but
they were unable to correct the problem so I decided maybe you all could
perhaps provide a solution of sorts or maybe you have had the same problem as
me. Sorry for the Lengthy post and the bad punctuation/grammar, but if anyone
could provide some sort of solution, it would be greatly appreciated. Thanks
in advance.

Ryan