For the past year I've been using an Airport Extreme upstairs to extend my wireless network. It's never given me any problems until two weeks ago when I unplugged it briefly to plug it into a battery backup (it was directly into the wall). Now it continually loses its connection to my Time Capsule downstairs that acts as the main router. I can power cycle the Airport and it fixes it for a while then it drops the connection again. What could be causing this?