Wirless connects but internet doesnt load

Hello,
hi i am having a problem with my laptop connecting to the internet. i just bought a used dell inspiron 1100 it has a fresh install of windows xp home. i tried the wireless internet when i bought it and it worked great.i have a linskys router at my home. all the other laptops and my ps3 work fine on the internet just this one doesnt connect to the internet. it pics up my router with a very strong signal. i have the security on the router disabled and it still doesnt work. when i hook up the laptop directly with a wire the internet works fine. when i try to go on the internet it says cannot find server or dns error. any help would be very appreciated as i am not the best with computers. you can even e mail me if you want to help Daynkuby@yahoo.com. thank you in advance.
dayn