Power off the Acer laptop and flip the unit over. Slide the battery release lever over and lift the battery out of the laptop.
Turn the laptop back over and open the lid. Look inside the
open area on the keyboard where the key would normally go. Check to see
if the plastic retaining clip is still inside the hole.
Locate the plastic retaining clip if it fell off the keyboard
along with the key. Use a pair of tweezers to set the clip back inside
the hole. Line up the holes on the clip with the four raised nodules
inside the keyboard hole.
Set the key back onto the plastic clip. Push the key down until it clicks into place.
Flip the laptop back over if there are keys that are not
working properly. Use the Phillips-head screwdriver to remove the three
screws on the left side of the case that hold the keyboard in place.
Turn the laptop back over so that you can see the LCD screen.
Push the thin end of a flat-head screwdriver under the LED
indicator strip above the keyboard. Pop the strip upward and pull it off
Lift the keyboard up towards you until the long ribbon cable
running from the bottom of the keyboard to the motherboard comes into
view. Unplug the cable from the port on the motherboard and then pull
the keyboard and its ribbon cable off the case. Spray out the underside
of the keys and the inside of the Acer laptop case with canned air.
Reassemble the keyboard, LED indicator strip and battery.
If I could be of further assistance, let me know.