# Remove both the battery and the charger
# Press and hold the power button for 10 seconds
# Re-connect the charger while holding the power button, keep holding the power button for 10 more seconds
# Re-connect the battery, try powering up your computer if it has not done so itself already.
This worked for my friend when he got no power after a battery replacement on his MBP. Hopefully this works for you too.