Mac That Won't Start

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Check to see that the power cable is properly connected to the computer and the outlet. You should also check to be sure that any power strips are on and working. Try starting your computer from several electrical outlets.
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Step 2

Press the "Caps Lock" button on the keyboard and see whether the green light comes on. If the light comes on, but your Mac won't start, the computer might be asleep and may need to have the power management unit (PMU) reset or serviced. Press and hold the power button for 5 seconds to see whether the computer will turn off or wake up.
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Step 3

Insert the the Mac OS X CD and hold the "C" key while powering on your computer to boot from the disc and not the computer's internal drive. Run Disc Utility from the CD to diagnose and attempt to repair some hardware problems. You can also erase the hard disc and reinstall OS X with this method, although you won't have a chance to back up your data.
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Step 4

Reset the power management unit by disconnecting the power cord from the back of your computer. Wait 2 minutes before reconnecting the cord and turning on your computer. Laptops and older computers have different procedures for resetting the PMU, which you can get from Apple's website (see Resources below).
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Step 5

Drain the logic board's battery on your Mac. Disconnect the battery (for a laptop) and the power adapter, then press the power switch and let the computer sit for about 25 minutes before reconnecting and booting it. This step forces the computer to reset its logic board and all other components that use the backup electrical charge.
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Step 6

Open your computer and remove any RAM upgrades that you've installed. See whether the computer starts up without the extra memory. Incompatible or incorrectly installed memory can make your computer unresponsive.


Tips & Warnings


You can connect your Mac to another one with a Firewire cable and then boot your computer in target disc mode by holding the "T" while turning it on. This mode can give you a chance to copy your important data from the computer while you troubleshoot it.