like the title says... my gf's iMac core duo 17" is intermittently not seeing our airport network. When it does see the network, it has 3 or 4 bars, so it's not signal strength. There are also several neighbors' networks nearby that disappear when ours does. Often a restart will fix the problem, but not always. Apple Hardware Test reports nothing wrong, but the iMac was recently shipped to us by a forum member here. I wonder if the airport card could have been jarred loose in transit? I don't know; I'm grasping at straws here. Why is this happening?