First try resetting your SMC.
- Make sure the Mac is plugged in to the power.
- Press and hold the Shift, Option, and Control keys on the
left side and press the power button.
- Release all the keys at once, and then turn the Mac on normally.
Then try resetting the PRAM (I know you need to hear a startup chime for this but try it anyways).
- Press the power button, and as soon as you hear the startup chime, hold down Command-Option-P-R.
- Keep holding down those keys until you hear a second startup chime. Then let go and allow your Mac to continue starting normally.
Credit:
http://www.macworld.com/article/2881177/how-to-reset-your-macs-nvram-pram-and-smc.html
-Sam