Dell 1545xp-3 wireless network adapter

Hello,
i m using dell 1545 with window xp sp3. i have downloaded all latest drivers from dell.my wireless adapter detect the network and shows connected and good signal strength with speed 54 mbps.but i m not able to access my internet through any browser moreover on ping default gateway it shows request time out.on right click connection it shows packet recieved zero and sent packet about 100. while with wired lan on the same network i m able to access internet,able to ping default gateway. moreover no virus is in my laptop.plz help me