I have an iMac connecting happily to my internet router with AirPort, but AirPort can't find my Time Capsule (which sits one foot away from the iMac). It was working OK, but a pop-up offered an update to firmware for the capsule which I downloaded - since when AirPort can't find the capsule. When it was working, it flashed yellow when the iMac was sleeping (and green when awake). Any suggestions please?