Go to start->control panel->system->hardware tab->device manager
is the devfice listed in the network adapters section?
if so right click device and check the status does it say "this device is working properly" try updating the drivers under the "driver" tab, if this doesnt work or the icon has a yellow triangle next to it? try uninstalling the device and reinstalling it (right click icon-> uninstall then right click "network adapters" and select "scan for hardware changes".
also check modem is not disabled in your network connections (control panel)
Also most laptops have a switch on the front or side which can turn off/on the wireless card, ensure this hasnt been switched to off by mistake (can you see a light on the laptop which indicates whether the wireless card is active or not)