Have you tried this tutorial ? that shows how to use gps or wifi Using the Location Sensor
Among other things it that how to force the use of gps or wifi (if that is what your really want to do) but I expect your issue is something else.
or tried How to put my location on a map
What you describe can happen for a LOT of reasons; primarily not knowing how to use the LocationSensor and Map together. You didn't show your Blocks so it is impossible to provide specific advice.