Most laptops with built-in wireless have a little light on them somewhere that comes on when wireless is turned on (even if it's not connected). Is that light on? Again, most laptops with built-in wireless also offer a quick way of turning it off by either a little switch somewhere or by a Fn-something key combination.
If you post what make/model laptop it is then I might be able to offer something more specific.
Sometimes the wireless connection shows up in the 'eject hardware safely' notification on the toolbar along with a USB drive or camera card you're trying to eject & it's easy to click the wrong one - I've known it happen with CD/DVD drives too. Generally they do reappear when you reboot.