Aporte original por: Mal ,
Try this. Disconnect all power sources. 1. Hold the 'option' key down. 2. Plug in the power source. 3. Keep holding down the 'option' key for about 5-seconds and then release. 4. Disconnect all power sources and wait for 10-seconds. 5. Plug in power source and power on computer. This has worked for me on countless occasions. Thanks to the guys at Stockley Park that told me this years ago.