Troubleshoot. Disable and re-enable the wireless adapter with either a toggle, button or software (depending on what you have). Still no dice? Reboot. Still nothing? hardwire the laptop to the network and check Windows updates. Nothing still? go to manufacturer website and go get the latest wireless driver.
Oh yeah, and make sure the wireless adapter is turned on. To do that, go to Control panel, Network and sharing Center, then Change Adapter Settings. If it says Disabled, right click and enable it. Still no dice? make sure that there isn't a switch on your laptop for Wifi that you may have accidentally switched off.
Hope that helps.