I had the same problem and resolved it by following the instruction for the 910 will not switch on question as follows: There is a hidden reset button that should fix the problem. Turn your tom tom upside down and view from the back. Locate the gold pins, starting at the end furthest away from the large round gold plug, count three along, now cast your eyes 10mm toward you, across the little bit of printed circuit board visible, to a J shape in the black plastic casing. In the center of that J shape is a tiny hole. Stick the end of paper clip or pin into that hole and you will press a micro-switch which will reset the tom tom. Swith the machine on, and it should start up without losing any of your saved settings.
Brian L, April 2008