Hmm,
Any chance that the laptop's internal wireless is transmitting using a different protocol to the Belkin?
Delve into the laptop's user manual to find out the specifications for the wireless link. (ie what is the Maximum encryption level possible)
Logon to the router's internal controls (in your web browser enter 192.168.0.1 as if you were navigating to a webpage) and search for a menu page where there may be a drop-down menu where you can switch the protocol to match.
(At least this is what I'd look at with mine: it's not a Belkin, so I can't be specific).
Look for drop-down selectors with things like "WPA2-PSK" which is the encryption level and see what else is on offer. Your computer might not be able to handle some of the options your router offers so just set it to one your computer can handle.
(Probably not the solution to your problem but just info for anyone else browsing this thread).
If you come across the ISP-specific protocol settings, don't adjust them (because they're known to be working) but do jot them down in a notebook for later reference. Your ISP customer service dept is the only place to go for advice on correcting mistakes in these settings.