said by tobicat: It sounds to me like your router has been set to the access point mode. ...the first thing I would try is to reset it back to factory defaults.
If your computer connects directly to the modem, that this is the next thing I'd do as well. Hold down the little reset button for 30 seconds on the router. Usually takes a pencil tip or something.
The router should work right out of the box. Be sure to setup WPA wireless security, a unique router name and pw as well, all that stuff, once it's working....