There are several places you can switch your LAN on. First is the BIOS. This is the screen you see when you first turn the laptop on. You'll need to tap the F2 (or potentally Delete or even F10 - read the text and it will tell you what to press to enter "SETUP") to enter this screen otherwise it will carry on and boot to Windows!
Have a look through the various options and ensure wireless LAN is "enabled". If you're having difficulties finding anything try posting back the model of laptop and we may be able to help.
Beyond that; Go to Network options in Control Panel and try double clicking the Wireless LAN. This will more often than not enable the connection
Best of luck