Step 1. Remove one AAA battery. Press & hold Clear button for 5 Seconds. Replace the battery and turn on.
if that doesn't work go to Step 2.
Step 2. Remove one AAA battery. Press & hold DEL button for 5 seconds. Replace battery and turn on.
if that doesn't work go to final step.
Step 3. Remove all batteries including the back-up battery for at least 5 minutes. After 5 minutes replace all batteries and turn on