Please help: Vista laptop connected to network, but not internet

>I have a desktop running XP, a Laptop running Vista, a Linksys wireless
> router, and a no-name cable modem provided by my ISP.
>
> Several months ago I set up a wireless network that was functioning
> perfectly until a few days ago. The XP machine can still access the
> internet
> through an ethernet cable connected directly to the router. The Vista
> machine
> seems to be able to connect to the wireless network, but not the internet.
>
> My wife says she didn't modify any of the settings on the Vista laptop,
> but
> I'm at a loss as to why it could connect to the internet a few days ago,
> but
> can't now.
>
> Right clicking on the networking icon in the system tray brings up a
> message
> box that says:
>
> Currently connected to:
> Unidentified...(motherbrain) [<-- the name of the network]
> Access: Limited Connectivity [but the signal strength is excellent...]
>
> The Network and Sharing Center shows the laptop connected to the
> unidentified network (though there is a yellow warning sign on the
> connection), but there is a big red "x" on the connection to the internet.
>
> Any help would be greatly appreciated.