Hello there! You can try the following to reset your mac. Also since your took it apart you will have to verify you didnt leave any loose wires ( look more at the charging port )
1. Shut down the Macbook .2. Plug in the MagSafe power adapter to a power source, connecting it to the Macbook if its not already connected.3. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.4. Release all the keys and the power button at the same time.5. Press the power button to turn on the Macbook.6. Press and hold the Command-Option-P-R keys before the gray screen appears.7. Hold the keys down until the Macbook restarts.8. Release the keys.