Are you getting indicator lights? Does it charge? Any signs of life when you press the power button?
If you get nothing at all, it's a good idea to discharge the power circuit. Remove the battery and AC cord. Hold down the power button for 10-30 seconds. Without letting go, reattach the AC cord and continue holding power for another 10-30 seconds. Release the button and try turning it on normally.
(On Windows machines, this is also a good way to clear the CMOS on some machines.)