Open system Preferences->Network pane and highlight the Airport card. See if you can turn it on or of from there.
If that doesn't work, first make sure you Airport card is turn off, and go back into System Preferences->Network pane, then look at the top of Network pane for the "Location" bar. Use the "Location" bar drop-down and select Edit location and in that pop-up click on the + button to create a new custom named Location, calling it whatever you like. Then after you make a new Location look near the bottom of the Network pane for the 'Apply' button.Click on the 'Apply' button to save your new custom Location.
Making this new Location will reset you Airport card preferences and IMHO is a little better at getting wireless points then the Automatic Location in the Network pane.
So give it try to see if clears things up for you, Good Luck.