Have a look at the connectors on the cradle and the zumo. Could be worth cleaning them up and then putting a smear of vaseline on them. If they're green, then they'll definitely need some attention. Before you pull it apart, you should post something in your local section and try a 5 min swap with another bike that is known to work. This will narrow your options down to zumo or cradle.
Yes I have my cradle went down at the start of this years trip to germany The Sat nav would still work on its own and in other cradles but no power to my cradle. After checking the cradle on my return one of the power supplies to the multi pin connector had failed (if you speak to Garmin help they will email you a circuit diagram of the cradle). I cant prove it but i believe it was caused by water ingress. I bought a new cradle from Garmin £40ish I think once fitted all was well.
Mike