Every now and then, I disable my wireless via the menu icon in Ubuntu. Then, when I try to enable the wifi, it tells me that "wireless is disabled" or "wireless is disabled by hardware switch". There is a red icon on the F2 key that looks like a wireless icon, and in Windows, pressing the (red) Fn key and F2 toggles the wifi. This does not work in Ubuntu, leaving me no clear way to turn wifi back on. How can I restart wifi in Ubuntu?