On a recent walk my GPS was performing perfectly when all of a sudden the screen blanked (no warning message) I assumed that the batteries were low so put in 2 new ones. GPS turned on again and displayed the menu. I selected 'map' and this duly appeared ... for about 3 seconds then blank screen! I have tried another set of batteries, same result. I removed the SD card and tried again, same result. I have tried to do a reset but to no avail. Has anyone got a solution?