i don't really know why but this worked for me a few times, but I haven't tried it with this problem.
Hold down the power button for 5+ seconds, disconnect all cords from the laptop, remove the battery and let it sit for 5 min.
Then connect all the cords again and reboot.
At the acer screen, press f12 (i think, whatever the button is that it says you can press)
and then continue the boot.
Hope it helps