Resetting the System Management Controller (SMC) on your Mac

Einleitung

The following symptoms may mean an SMC reset is needed:

Your computer's fans are running at high speed, even if the computer is not under heavy load and is properly ventilated.
Keyboard backlight works incorrectly.
Status light, if present, is malfunctioning.
Battery LEDs, if present, work incorrectly (for Mac laptops with a non-removable battery).
The display backlight does not react correctly to changes in brightness.
Your Mac does not respond when you press the power button.

* Your Mac laptop does not respond properly when you close or open the lid.

* Your Mac goes to sleep or shuts down unexpectedly.

The battery does not charge properly.
MagSafe Power Adapter LED does not indicate correct activity.
Your Mac is abnormally slow, although its processor is not heavily used.
A computer that supports the target display mode does not switch between modes as expected, or switches between modes unexpectedly.
Mac Pro (Late 2013) I/O ports are not illuminated when moving the computer.

Try each of the following steps in the order listed before resetting the SMC. Check after each troubleshooting step if the issue still persists.
If your Mac isn't responding, force shut it down by pressing and holding the power button for 10 seconds. Any unsaved data in open applications will however be lost.
Press Command+Option+Esc to force quit any unresponsive app.
Put your Mac in sleep mode by choosing Sleep from the Apple menu. Wake the computer after it went to sleep mode.
Restart your Mac by choosing Restart from the Apple menu.
Shut down your Mac by choosing Shut Down from the Apple menu, then turn it back on.

If you're using a Mac laptop that's having power or battery issues, follow these steps:
Unplug the Mac's power adapter and power outlet for a few seconds, then plug them back in.
Shut down your Mac.
Remove and reinsert the battery (if removable).
Restart your Mac.