How can I troubleshoot a MacBook that won't switch on?

Unplug the power adapter from the electrical outlet and from the MacBook. Wait one minute. Plug it back into the wall first, then to the computer. Make sure the electrical outlet is working by plugging in another device (such as a lamp). When you plug the adapter back into the computer, the power adapter LEDs should light up green or amber. Press the control key, the command key, and the power button simultaneously and hold for three seconds to try to restart the computer.

Reset the PRAM. After pressing the power button, hold down these keys simultaneously: Command-Option-P-R, until you hear the startup chime at least one additional time after the initial startup chime.

Reset the SMC for the MacBook And MacBook Pro by removing the AC power, removing the battery and then holding down the power button for five seconds. If none of this works then the first thing to check is the keyboard to logic booard connection as the machine may not be getting a signal to turn on.