By 'activate', do you mean enable or turn on? First, check that your hardware wifi switch is turned on. This is usually located on either the front of the laptop or, on the keyboard somewhere near the top where the function keys are. If your wifi still does not work after turning on your hardware switch, then it might be a driver problem. To check for a problem open up the Device Manager by going to Start-->Search for 'Device Manager'-->Click on 'Device Manager'. Then expand the tab 'Network Adapters' and see if there is a yellow exclamation point next to your wireless adapter.
Hope this helps,