Cannot connect to the internet

Inspiron B130 running xp home (probably not the latest and greatest version). It shows that I am connected to internet via my router and says signal strength is excellent (3 other laptops in the room connect to internet with no problem). Successfully installed Firefox via memory stick. Click on Firefox icon and the Firefox Home Page comes up with the Google search box. I type in the address that the other 3 laptops use to access the internet, and it comes back "Server no found". My Dell Wireless card/connection shows connected, but the laptop can not find the router.  Any help appreciated...