Reset Your Apple Mac’s PRAM:

1) Switch on the macbook, immediately hold down together OPTION, COMMAND, R, P on your keyboard.
2) Once you hear Mac reboot sound you can release the keys.
3) It will reboot twice and should start as normal if issue is resolved.

Reset Your Apple Mac’s NVRAM:

1) Shut down your Mac.
2) Find Command, Option, P, and R on your keyboard. (if you do not have a command button on keyboard ‘ please kindly use the ‘Windows’ key). You would need to use a wired keyboard – a standard PC USB keyboard will work.
3) Turn on your Mac.
4) Press and hold the Command-Option-P-R keys immediately after you hear the startup sound.
5) Hold these keys until the computer restarts and you hear the startup sound for a second time.
6) Release the keys.

Reset SMC on Apple Mac:

1) Shut down your Mac.
2) Disconnect the power cord.
3) Press and hold the Mac’s power button for 5 seconds.
4) Release the button.
5) Reattach the power cables and boot the Mac as usual.