Sounds like you could have an issue with your logic board. If the system has a known good battery and charger, and you've performed an SMC reset, and it is still unable to power on, it is likely due to a hardware issue with the logic board or another component attached to the logic board. You could try disconnecting components and then attempting to power on in different configurations to see if you can isolate the failed component, but if it doesn't power on in any configuration then you probably have a failed logic board. At that point you could inspect the board for signs of damage or you could consider replacing the board. Good luck!