Try a hard reset maybe?
I think the method is:
"Hard Reset
Remove the main battery and the backup battery, wait for approximately 3 minutes, then reinsert them. Insert main battery before back-up battery. Remember, leaving the palmtop PC with no power causes ALL DATA TO BE LOST."
via
https://manualmachine.com/hp/620lx/910123-user-manual/Edited by stingraze 2021-06-21 6:01 AM