|Some laptops have a separate switch, others use a key combination (Fn and one of the F keys). Your user manual will tell you which you need.|
If you are sure you've turned it on and you still have no network found then click on 'network and sharing center', then 'change adapter settings' and see if your wireless is listed & what state it is in. If the card isn't shown then check in device manager to see if it is listed but with an asterisk against it.
If you still can see no trace of the wireless adapter then you need a tech to look at it, to make sure it's installed & connected.
"I've always been mad, I know I've been mad, like the most of us..." Pink Floyd