I have found in the past that if you go to another country via air then switch gps on it can take anything up to half hour to get a signal.
Make sure the clock is at the correct time,and leave unit switched on with a good view of sky.If poss outside of car.I am sure it will lock on given time.

Or simply connect to the PC, start TT Home and click "update my device" to download the latest GPS data.