carfranz

Como no des un poco más de información...

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Sigue estas instrucciones en inglés a ver si así se resuelve tu problema:

PRAM & SMC resets
1. From the Apple menu, choose Shut Down (or if the computer is not responding, hold the power button until it turns off).
2. Unplug all cables from the computer, including the power cord and any display cables.
3. Wait at least 15 seconds.
4. Plug the power cord back in, making sure the power button is not being pressed at the time. Then reconnect your keyboard and mouse to the computer.
5. Press the power button on the back to start up your computer.

Resetting PRAM and NVRAM
Shut down the computer.
Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
Turn on the computer.
Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the second time.
Release the keys.