My lights have been flickering for the past few days, then I lost all power in a portion of the house. No breakers tripped, and the lines to the breakers and the neutral are all tight. When the power goes out I can hear a humming noise coming from the central air conditioner coil in our attic. When I shut the breaker to the air conditioner, after a minute or so the power comes back on in the portion of the house that was out. If I flip the A/C breaker on again, I get the same flickering, etc. The flickering can go on for days before losing power. Strange, any ideas?