One method of doing a hard reset is to remove the power cord and press the power button for 20 seconds.
Another method is, with a low battery and while charging, press and hold power button until the battery LED is off, then immediately pull the cable, release the power button, and try to power it on again.
+
+
UPDATE: Ok, I know this is an old thread but since that didn't work - have you checked the RAM?
One method of doing a hard reset is to remove the power cord and press the power button for 20 seconds.
Another method is, with a low battery and while charging, press and hold power button until the battery LED is off, then immediately pull the cable, release the power button, and try to power it on again.