I've had a similar issue but with the weirdest twist:
I have two Mini LUX's (connected to a Roamio Pro). A couple of weeks ago, LUX #1 (only 8 months old) stopped working..it would startup and show the first "Starting up" message and then die. I knew the problem was inside Lux #1 because, when I connected my LUX #2 to the same location, LUX #2 would work just fine.
So I contacted TiVo support and they eventually agreed to send me a new shrink-wrapped TiVo LUX as a replacement (for the $39.95 fee). I got it and it worked fine... but only for 5 days!! At that point (which is today), the new LUX #3 died with the EXACT same symptom as old LUX #1. And once again, when I swapped it for my old LUX #2, the old LUX #2 worked at the same location.
How can this be....how can a brand new LUX develop the exact same symptom as the one I returned...after just five days of use...while my other LUX works in the same location just fine? It makes no sense. HELP!
P.S. I will be calling TiVo tomorrow.