mac will not turn wi-fi on

My Mac will not turn wi-fi on. In the top right hand corner there is a wi-fi triangle with no bars in it. When I go to system preferences and click network it says Status:Off and then a button to the right of it saying Turn Wi-fi On. But when I click the button to turn the wifi on, nothing happens. It turns blue for a second and then nothing. It will not let me turn wi-fi on. PLEASE HELP. I have tried deleting wi-fi off my computer and and then adding it back on, it did not work.