any one every had a sat nav go wonky as mine seems to have i know its old. it is a garmin etrex, and it does not seem to able to lead you to a grid ref now.
Try a factory reset, I am not sure what model of Garmin etrex you have, but if you google hard reset for your model of etrex you will find instructions on how to reset it to the factory defaults, this may fix it. Also note this will wipe all your current settings / waypoint of the device.
Colin
Everyone has a photographic memory. My problem is I don't have any film.