Solution: Battery charge is too low. Connect unit to a wall supply for a fresh charge and turn on. Power errors can be caused by any number of issues.
If the unit will not power on, validate that the power adapter is plugged into both the unit itself as well as working power outlet. If the unit is still not powering on, instruct the patient to test it with a different power outlet.  If the unit is plugged into a surge protector power strip, direct the patient to disconnect it from the power strip and plug it directly into the wall.
If the unit is still showing no signs of power, it will need to be replaced.