You don't say what make your PC is and so it is difficult to give other than generic help. Some laptops have a small switch to turn WiFi on and others require a keystroke sequence. (Some older ones have a software utility.)
All of them have a how to in the instruction manual. If you do not have a paper copy, then it is often on the hard disk of the laptop or can be downloaded from the manufacturer's web site.
T, June 2009
