There is a small reset button on the back of the monitor, please insert a paper clip or similar. This will unfreeze the monitor and you will not lose any data.
Freezing can be caused by a build up of workout data. We would advise clearing the memory on your Wattbike monitor by going into Recall > Old Workout Data > Press Menu > Delete All Workouts.
If the problem continues please contact our Distributor who will be happy to assist.