NVRAM or PRAM

If you are having issues with sound volume, display resolution, startup-disk selection, time zone, and recent kernel panics resetting the NVRAM or PRAM on your Mac may help resolve the issue.  The NVRAM or PRAM in the computer store information, by resetting this it can resolve some issues.

Apple’s page on resetting NVRAM or PRAM – https://support.apple.com/en-us/HT204063
Or you can go into your Applications folder, Utilities folder and open Terminal type in nvram -c and press Enter. Restart your Mac to see if this has helped.

SMC – System Management Controller

The SMC System Management Controller can help with issues – responding to presses of the power button, responding to display lid opening and closing on Mac notebooks, battery management, thermal management, sudden motion sensor, ambient light sensor, keyboard backlighting, status indicator light, battery status indicator.

Apple’s page on resetting SMC – https://support.apple.com/en-us/HT201295