Unfortunately, I can't get any of your suggestions to work. If I restart the computer and go through the Network Diagnostics set-up, I can sometimes get it to find my home network and connect, though not everytime. The connection might last from 2 minutes to an hour or more, but then it is inevitably lost, and Airport shows no available networks, even though my MacBook is still connected to my home network and shows several other available networks from neighbors' houses, too. It seems like it must be a software problem since I had no problems before the update. Does anyone know anything else I can try short of taking it in to an Apple Store? Thanks for all your suggestions.