If you have been using android devices for a long time, these types of errors are well known. Try the instructors below:
# Switch off the tablet
# Press and hold the Power key after the model name appears on the screen.
# Release the Power key when Acer is displayed on screen.
# After removing the power key, press and hold the volume key down.
# Maintain the key down volume until the device fully restarts.
# Remove the down key volume from the lower left side of the screen if safe mode shows.