If the battery has become very flat (low), it may take a little longer for the unit to show that it is charging. First please make sure the unit has “clicked” into place on the charger so that the silver contacts are aligned together. Then make sure you give the unit at least 30 minutes for the “charging” to appear on the screen. Typically after 30 minutes you should see a change from a blank screen to “charging”. If the unit is still not responding after more than 30 minutes on a charge, please contact NK for assistance.