Check within security on the lappy for the correct WEP/WPA key code (this assuming you have security enabled).All security settings from the host pc must be carried over to the laptop.
If using XP,
Start / Control Panel / select Wireless Network setup Wizard.Follow the prompts.
If you can access the router's configuration page,for example open your browser and type 220.127.116.11 into your address bar,this will allow you to change any configurations or reset some/all.
The make/model of the router would help us more if possible.