I had a similar issue with a MacBook Pro 13 A1278. Would not power on. Pressing Shift, Control, Option and power button did nothing. Disconnecting the battery and then connecting the power lead would instantly turn the laptop on without pressing the power button. I could then re-connect the battery and disconnect the power lead and it would contine to work. But if I shutdown the macbook it would not restart without disconnecting the battery and repeating the same process. I eventually tracked it down to a faulty keyboard. It’s worth noting that the power button is part of the keyboard! After replacing the keyboard which required dissmantling the macbook (not as bad as it sounds if your handy with a screwdriver) and then removing a further 51 screws required just to replace the keyboard. There a plenty of good quality videos on YouTube showing how to. Now everything is working perfectly :)

I had a similar issue with a MacBook Pro 13 A1278. Would not power on. Pressing Shift, Control, Option and power button did nothing. Disconnecting the battery and then connecting the power lead would instantly turn the laptop on without pressing the power button. I could then re-connect the battery and disconnect the power lead and it would contine to work. But if I shutdown the macbook it would not restart without disconnecting the battery and then repeating the same process. I eventually tracked it down to a faulty keyboard. It’s worth noting that the power button is part of the keyboard! After replacing the keyboard which required dissmantling the macbook (not as bad as it sounds if your handy with a screwdriver) and then removing a further 51 screws required just to replace the keyboard. There a plenty of good quality videos on YouTube showing how to. Now everything is working perfectly :)