did you have a router before? if so did you name the wireless network the same and used a different key phrase? did you check the spelling of the key phrase?
Windows key plus R in Vista and Windows 7, then type in the following, including all the spaces:-
cmd /k ipconfig /all
then press Enter and from the black form that shows up, take a note of the numeric code beside the IPv4 Address.
what is the IP that you where assigned?