Troubleshooting macOS Sierra Problems

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If you need to reset the SMC!” You have tried rebooting, you’ve reset the PRAM,

If you need to reset the SMC!” You have tried rebooting, you’ve reset the PRAM,
Here's how to reset your 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.
 you’ve done it all, but your Mac is still behaving strangely. What next? In certain circumstances, resetting your Mac System Management Controller (SMC) can be a solution. This is sometimes necessary to restore normal lower level system functionality to your Mac, particularly for power and hardware related troubles.

We’ll show you exactly how to reset the SMC on any type of Mac (and any version of OS X) and the type of problems that it may resolve.

When & Why Reset SMC on a Mac?
Typically, an SMC reset helps to resolve many power and hardware related issues that are otherwise unresponsive to troubleshooting techniques. Resetting a Mac SMC is particularly effective if you’re having the following types of problems:
* Issues with your Mac cooling fans and fan management: the fans run constantly at high speed, fans run high despite low CPU usage and adequate ventilation, fans not working at all, etc
* Power management and battery problems: Mac isn’t turning on, sleep isn’t working, random shutdowns and reboots, battery isn’t charging, Mac won’t wake from sleep, etc
* Light problems and improper lighting management: battery indicator lights aren’t working, display backlighting isn’t adjusting to ambient light changes, keyboard backlights not working, etc
* Video and external displays not working: display brightness functionality not working properly, target video mode isn’t working properly, external display isn’t working, etc
* General performance and functionality problems: abnormally sluggish behavior despite no CPU or disk usage, external ports not working, airport & bluetooth aren’t showing up, external devices are not being found, etc

Reset SMC of a MacBook Air, MacBook Pro Retina, or MacBook Pro’s with an internal non-removable battery
This is how to reset SMC on most modern Mac laptops, none of which have a removable battery:
  1. Shutdown your MacBook Air / MacBook Pro 
  2. Connect the power adapter to the Mac 
  3. On the MacBook / Pro’s keyboard, hold down the Shift+Control+Option keys and the Power button at the same time 
  4. 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 
  5. Boot your Mac as usual 
Here’s the key sequence to hold down:

Do keep in mind that by resetting the SMC you will lose power specific settings, like the time it takes to sleep a Mac and other customizations to power settings. No big deal, but if you have made many changes to your hardware behavior you will want to adjust stuff like sleep behavior again.
The boot time after resetting a machines SMC can be a bit longer than usual, that is normal.

Reset SMC of an iMac, Mac Pro, Mac Mini
Resetting SMC is different for non-portable Macs.
On any desktop Mac, here is how you reset the System Management Controller:
  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 
Reset the SMC of a MacBook or MacBook Pro’s with detachable batteries

Older MacBook laptops, indicated by having a removable battery, can reset SMC with the following approach:
  1. Shutdown the MacBook/Pro and remove the battery 
  2. Disconnect the power adapter, hold the Power Key for 10 seconds 
  3. Release the power key and reconnect your battery and power adapter 
  4. Turn your Mac on 
  5. Let boot as usual 
What is SMC anyway?
SMC stands for System Management Controller, a critical low-level component on Mac hardware. Much like the name sounds, the SMC controls and managements system hardware for power consumption, battery charging and battery function, thermal activity and fan activity, LED lighting for keyboards and displays, GPU functionality with video mode changes and video output, sleep and wake, and other core hardware functionality on a Mac.