check the output of your AC adapter if it is giving out the correct voltage.
if the AC adapter is giving out correct voltage, it could be that your power ON button is defective or the switch is dead, or it can be the motherboard. i suggest you check the power ON switch (can be part of the keyboard or on a separate panel). also check the cables connecting the switch to the motherboard if present. best if you have a working spare to swap the power button/switch.
here is the link to the service manual, should decide to fix it yourself