|re' the computer in question: Is there an icon in the system tray (bottom right corner) to show the cat-5/ethernet connections is active? Similarly if you're trying to use wifi there will be one there for that as well. Wifi is by default (invariably) not enabled on a router when you first set it up/receive it; you have to enable wifi manually.|
Two approaches to start with perhaps?
Presuming the dsl/broadband connected and stable light is showing just that; reboot the router.
If still no joy...,check in device manager to see if there are any errors showing in the network adapter section:
If there are any yellow exclamation marks in that (networks adapters) area... post back... Likely you may need to remove/uninstall and re-install the adapter (this is a simple software routine - not an actual physical removal of the adapter).