"Limited or no connectivity" network did not assign a network addr

Please help i have been trying to fix this for 2 months every suggestion i
have seen has not worked i have a Acer TravelMate 4052LCi my router is a
Linksys Wireless-G Broadband Router model number WRT54G incase you need to
know i am with ntl broadband. I am just trying to provide as much information
as i can. i know there is nothing wrong with my laptop because i took it back
to the shop so someone could look at it but he said when he tried it with
other networks it worked so its obviously something wrong with the network
but i dont know how to assign a network address. Also i havent got windows xp
sp2 and i have no viruses, adware, spyware, trojans or worms on my computer
and laptop im sure of that.