Try resetting the SMC
Connect the power adapter to the Mac. On the MacBook / Pro's keyboard, hold down the Shift+Control+Option keys and the Power button at the same time. Release all keys and the power button at the same time – the little light on the MagSafe adapter may change colors briefly to indicate the SMC has reset.
That failing zap the PRAM
Shut down your machine. Yes, all the way down, not sleep or logging out.
Press the power button and then press command-option-p-r. ...
Hold those keys down until your Mac reboots again and you here the startup chime.
Let go of the keys and let your Mac reboot normally.