Make sure you have run this update:
You can check by going to System Preferences/ software update, installed tab. (You can also run it again safley) Always do a back up before doing anything.
You can also try a NVRAM/PRAM reset:
Power off, power back on holding the following keys, OPTION + COMMAND + P + R
continue to hold these keys till you hear the start chime 2 times, reboot.