Reset your Mac's PRAM by shutting it down, press the keys Command, Option, P and R and allow the Mac to reboot regularly. You may have to readjust many of your personalized settings after PRAM is reset. The Next Web recommends resetting the SMC as well.Continue Reading
Fully shut down your Mac. Next, press the power button and immediately press and hold the Command, Option, P and R keys. Make sure these keys are pressed before the gray screen appears; otherwise, you must try again. Continue to hold these keys down, and the Mac should reboot again. Do not release these keys until you hear the startup chime. Finally, allow the Mac to boot up normally.
After resetting the PRAM, you may have to fix your preferences, such as mouse speed, timezone, alarm settings and other options. If the problem persists, you may have to reset the PRAM multiple times.
Techniques to reset SMC vary depending on the power source, such as if the computer has a removable or unremovable battery or if it uses a power adapter. For a device with a removable battery, fully shut down the computer, remove any plugs and the battery, press and hold the power button for five seconds, and reconnect your system.