If you haven’t already, try to power on the machine with a separate known-good charger connected. If this doesn’t work, you most likely have an issue with your battery, MagSafe board, or logic board. Try disconnecting the battery, connecting the charger, and pressing the power button. If the machine is able to power on with the battery disconnected and run off of charger power you probably have a bad battery. If you have a friend with a compatible model you can try installing their battery to see if it resolves the issue. If you aren’t able to get any signs of life with the battery disconnected, you can read the voltage on the MagSafe board with a multimeter to see if it’s passing the right voltage. If it’s not passing enough voltage you probably have a failed MagSafe board. If it’s passing too much voltage you probably have a short on your logic board.