I've had this problem twice already, running 10.4.8. My airport menu on the menu bar suddenly displays no networks, and cannot find any, after logging out sometimes and logging back in. The only way to fix this is to reset the computer. Upon resetting the iMac, I've also discovered that the time, volume, and fast user-switching fields go missing too. I have to go into system preferences, and click the check boxes to display them again. Has anyone else had this problem with 10.4.8 and the airport update (assuming that's causing it)? By the way, it is an intel imac core duo 17", with an airport express as router, with WPA2 protection. EDIT: It just happened! Literally! There's no outside interference, such as phones or microwaves, the airport just went dead, and no wireless networks were available. My airport express was green the whole time, and running.