OS X V10.7 Lion :: Wireless On Imac Won't Display Any Network SSID's

I have an older imac running Lion 10.7.4.My router is a Time Capsule running 7.6.1. Yesterday my imac randomly disconnected from wifi and hasn't been able to reconnect since.When I click the wifi icon no networks show up in the list; it simply shows a greyed out "No Network My iphone and laptop each show 5 networks in the area including my own, the imac shows none.I even set my iphone up as a pesonal hotspot to see if the SSID would show up - it I tried putting my network name in manually through "join other network"- nothing. I have reset the computer and router several times each As far as my imac is concerned there are no wireless signals available.

So here's the odd part, I assume the wifi card has just died and haul my imac into the nearby apple authorized repair center. The guy plugs it in and it works no problem - shows the store's network and another one nearby and connects right away. The guy ran one or two quick tests but everything's working fine. I bring it home, the problem comes right back - can't see any of the wireless networks.Works fine through ethernet.