Disconnect AC adapter
Hold the power button for 15 seconds to clear the CMOS. Now hold the power button down and connect the AC adapter. The lights should come on for about 5 sec. then go off. Release the power button.

or

1. Unplug AC adapter and remove battery for 3-5 minutes.
2. Hold down the Insert/Scroll key on keyboard.
3. While holding down the Insert/Scroll key, press and hold the power button for about 15 seconds. (You will see the lights flash and then turn off)
4. Release the keys and boot normally.