Need more details.
Light turns on when you plug it in?
Battery has any power?
Does it make a dong noise?
Has the PB been opened up?
Does the PB smell burnt?
Does it make a long beep noise? Any beeps at all?
If the computer is plugged in and makes no dong or beep when you push the power button. Then the motherboard is finished.
If the PB has been opened up, check the connection of the power button to the motherboard.