MacBook Won't Boot Up

Even if you have a strong green led on the AC adapter tip the magsafe DC in board could be the culprit. Did you test it ? Also did you try a known working AC adapter ?

If you have a multimeter find the two power pads (left side of the top case connector) and with the multimeter settled to DCV/20 put the black probe on any logic board screw for ground and the red prob on one of the power pads. With the AC adapter connected you should get 3.42 volts one one pad and 0 on the other. Any other reading means something is wrong with the power line. Disconnect the top case ribbon cable from its socket and redo the voltage reading on the power pads. If you then get the 3.42V you'll know that the top case is faulty. If you still don't get the right voltage then remove the logic board and check the magsafe DC in board and the main power fuse. When connecting or disconnecting anything on the logic board make sure the AC adapter and the battery are not powering on to the Macbook.