No GPS signal on wired tom tom with 3970 ipaq

All was working well until this weekend after I arrived at my daughters for the weekend. The unit was left on for around 48 hours in my car and was working when I arriveed. However when returning to the vehicle I switched on and no GPS signal!
I have tried different dedicated leads and re loaded software all updated onto ipaq with no success. The tom tom gps receiver (the square shape) has a red light flashing? and if I disconnect and re-connect a brief green flash is observed.
Has the unit overheated by being left on unused for 48 hrs and overheated the receiver?
Can anyone help please
Thanks,Tony Clarke