2008 electrical system goes dead 1 second after turning ignition on

[lancastered5]

My wife's explorer has left her stranded three times now over the last 6 weeks. When the ignition key is turned to start the car, everything appears fine, dash lights come on, etc. for literally 1 second and then car goes completely dead. There is no power to anything. It's as dead as if the battery had been completely removed. The first time I checked the battery and because it was 6 years I old replaced it. A month later the problem reoccured. Removed the alternator and had tested. It was bad and I replaced it. Two weeks later a third occurrence. Cleaned the battery terminals and positive battery connections at the fuse box. It started after a rest of several hours after the second and third events. Didn't try it after the first event as I just assumed at the time the battery was dead so I jumped it with cables without trying it first. When starting it after the third event there was a short clicking sound (1-2 seconds) but then it started right up and have had no problems since. This last time I did notice that the clock time and the radio station presets were lost indicating a complete loss of power to the radio.