Wifi card turns off on macbook

[belmere]

Help! I'm at Uni and for the second time in a fortnight, my wifi card has turned off and I can't access the Internet at Uni. When I go home it's fine and sometimes here at Uni it's fine, some days this happens. It's that the wifi is grey, it's empty like wifi is off and it won't connect to anything.

Any ideas? Thank you !

[bennyling]

Your description of the icon is a little confusing, but what happens when you click on the icon?