How to Clear the PMU 1. Step 1 Quit all of your active applications and shut down your Mac. 2. Step 2 Once your computer is completely shut down, disconnect the computer's AC power Adapter and remove the battery from your Mac. 3. Step 3 Press and hold down the power button on your iMac for at least five seconds and then release the power button. 4. Step 4 With your Mac still shut off, reinstall the battery in your MacBook or MacBook Pro and reconnect the AC Adapter. The PMU/SMU has now been reset on your computer.
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How to Clear the PMU 1. Step 1 Quit all of your active applications and shut down your Mac. 2. Step 2 Once your computer is completely shut down, disconnect the computer's AC power. 3. Step 3 Press and hold down the power button on your iMac for at least five seconds and then release the power button. 4. Step 4 With your Mac still shut off reconnect the AC power. The PMU/SMU has now been reset on your computer.
Next try resetting the PRAM. Start up and immediately hold down the option - command and the "P" & "R" keys. Wait till you hear three tones, then let it try to start up.
How to Clear the PMU 1. Step 1 Quit all of your active applications and shut down your Mac. 2. Step 2 Once your computer is completely shut down, disconnect the computer's AC power Adapter and remove the battery from your Mac. 3. Step 3 Press and hold down the power button on your iMac for at least five seconds and then release the power button. 4. Step 4 With your Mac still shut off, reinstall the battery in your MacBook or MacBook Pro and reconnect the AC Adapter. The PMU/SMU has now been reset on your computer.
Next try resetting the PRAM. Start up and immediately hold down the option - command and the "P" & "R" keys. Wait till you hear three tones, then let it try to start up.