I highly recommend trying to reseat the Airport card. Many problems can be solved by this because even though you may think it is inserted all the way, you may not have gotten the final little "click" that it is all the way in. When the card is properly in all the way, the end of the card is flush with metal around the opening for the card. If any of the card is visible, it is not in all the way. Try pulling it out and then push it back in until it is fully seated.
Steve