Try performing an SMC reset and see if that helps. Steps on how to perform it:
1. Make sure the MacBook is shut down.
2. Plug in the MagSafe or USB-C power adapter to a power source and to your Mac.
3. Using the built-in keyboard, press Shift-Control-Option on the left side of the keyboard, then press the power button at the same time. Hold these keys and the power button for 10 seconds.
4. Release all keys, then press the power button again to turn on your Mac.
For more information about resetting the SMC visit this page:
https://support.apple.com/en-au/HT201295