Let’s try this again, disconnect the battery and anything else in the ports. Now press and hold the power button for a good 15secs that fully discharges the logic board - Hard SMC reset.
Now just plug in the MagSafe charger, at this point the system should spontaneously boot, did it?
If not it sounds like a messed up EFI boot loader. Apple did have a bad OS update release. What is the macOS release you are working with here. Did you do a OS update?