How To Fix Common Mac Startup Problems [MacRx]

Clues to the causes of Mac startup problems can be found by analyzing when in the boot process the system fails.  Problems may be related to the power supply, battery, hard drive, logic board, OS corruption or an issue with a user account.  Macs are reliable machines, but like many of us they get cranky from time to time.

Isolating where the problem is occurring is key to finding the solution.  Unplug any external peripherals (disk drives, printer, etc.) to help narrow down the cause.

The following questions are helpful to narrow down the cause of your Mac’s lethargy:
Does the System Turn On?
If your Mac won’t power on at all, likely suspects are a failed power supply, a bad logic board, a blown fuse (on desktops), a dead battery or a bad AC adapter (on portables).
Failed power supplies are sometimes accompanied by a popping sound.  That’s usually a capacitor which has given up the ghost and burst open.  iMac G5 systems frequently suffer from bad power supplies.  Supplies can fail fully or partially – they may give some power to the fans and such but still not work properly.  Fortunately a power supply or AC adapter is relatively inexpensive to replace.
Laptops have an additional power supply in the battery.  A dead or defective battery can prevent your MacBook or PowerBook from booting, or the battery may keep your system running after a crash, unable to reboot.  For laptops that have removable batteries (a dying Apple breed) remove the battery and unplug the computer when troubleshooting.

Macs also have another battery, called the PRAM (or NV-RAM) battery, that saves things like network settings, choice of startup drive, etc.  If the date and time reset each time you unplug the Mac you need a new PRAM battery.  A dead or dying PRAM battery can prevent a Mac from booting or cause erratic behavior.  Sometimes plugging in the computer and letting it sit for 30-60 minutes recharges the battery enough to permit booting.
Does it Make Any Noise?
Listening to your computer may seem a bit metaphysical, but can provide helpful clues to startup problems.  If your Mac doesn’t make any noise at all when switching it on, or if  you hear the fans running but nothing else, you may again have a power supply or logic board failure.
Sometimes a Mac will power on but the hard drive will squeal, whine very loudly or make ticking sounds. This can indicate a failed or failing hard drive.  Sometimes switching on/off a few times can help, but don’t push things under these circumstances.  Leaving a failing drive struggling too long can cause further damage
If you have a very old Mac with a non-spinning hard drive, more drastic measures may be required.  Some people have had success freezing a drive to fix this problem, but I haven’t tried this method myself.  If you have to resort to these types of tricks to get your disk working, copy any important data off a disk immediately when it’s accessible to be safe.
A groaning or buzzing sound that revs up and down at low RPM (and sounds like a wounded animal) could be a fan undergoing a slow death.  These components are inexpensive to replace.

Startup Tones and Blinking Lights
The Mac’s distinctive startup chime is more than an aural brand, it indicates a successful hardware (POST) test.  If you don’t hear the chime but instead hear a single tone, a series of tones, or see blinking lights, your Mac is indicating a hardware problem.  This may be the logic board, bad RAM, the power manager, a video card, etc..
Bad RAM can be a common culprit – on newer Macs, a blinking sequence of lights at startup can indicate this condition.  Fortunately this is easy to test for:  shut down the computer, remove one RAM DIMM at a time (remove in pairs on the Mac Pro or PowerMac G5), then reboot.  Repeat for each DIMM in succession until you find the culprit.  See your Mac Owner’s Manual (or Google for instructions) on to remove and install RAM.
If RAM isn’t the issue, check the Apple Knowledge Base for information.  Unfortunately non-standard startup tones often require a trip to a Mac service center for further diagnosis.  These tones are the “Check Engine” lights of the Macintosh world.
Once the screen turns grey the hardware tests are complete, and the Mac looks for a boot volume. Software now dominates the startup process.

Flashing Question Mark with Folder, or Circle/Slash
The flashing question mark or a circle/slash means your Mac can’t find a valid startup disk.  This can indicate a corrupt installation of Mac OS X or a failed (or failing) hard drive.
A pass through the excellent DiskWarrior utility is highly recommended for any disk-related startup problems.  You can also try Apple Disk Utility or another third-party utility like TechTool Pro or Drive Genius to try to repair the disk. If the drive is OK after repairs but the Mac still won’t boot, do an Archive & Install of Mac OS X to replace the operating system.
When the Apple Logo appears your Mac has found a valid system disk, and Mac OS X begins loading.

Apple Logo with Spinning Gear
Once the spinning gear appears the BSD kernel (Darwin) has assumed command and begins loading device drivers.  Shortly thereafter it transfers command to the almighty (and controversial) launchd process.  Such are the workings of UNIX.
What this means for us mortals is that when a Mac stalls at the Apple logo or the logo with a spinning gear, it probably has a corrupt Mac OS X installation.  It may also be having trouble accessing an internal or external hardware component, but this is less-likely.
Rebooting your Mac in Safe Mode can sometimes get things working well-enough that a second, normal reboot then works normally  Hold down the Shift key at startup to boot in Safe Mode.  DiskWarrior is also worth a shot (this is by far my most used disk utility).  If that doesn’t work, an Archive & Install may be needed.
Blue Screen or Blank Desktop
After the Operating System has finished loading the loginwindow process manager takes over and deposits you at your desktop.  A hang at a blue screen, at the login window, or at the image of your blank desktop often indicates a Problem with a User Account.  Corrupt Fonts or bad Preference Files (.plist) are common culprits.
Setting up a second, emergency admin account on your Mac is helpful for troubleshooting account problems.  Safe Boot may help too, as that bypasses non-essential fonts and user startup items which you can then remove from your User Library folder
Kernel Panic
“You need to restart your computer.”  No ifs, ands, or buts.  Presented in your native language, or something close.
A kernel panic is an Operating System crash with an historically colorful name.  Mac crashes can take on all sorts of appearances – the Spinning Beach Ball being perhaps the most familiar – but Apple has succeeded in scaring the bejesus out of many users with this dialog.  It is accompanied by the screen slowly darkening from top to bottom before a multilingual warning appears:

A kernel panic can happen at virtually any point in the boot process and may indicate a corrupt OS, an incompatible kernel extension, or a hardware problem.  Try a Safe Boot to disable non-Apple extensions.  If that doesn’t work try disconnecting peripherals, removing RAM, PCI cards, etc..  More good info about kernel panics can be found at The-X-Lab.

Boot from Another Drive to Troubleshoot

If your Mac has an optical drive (aka SuperDrive – most do) you can boot from an Apple software install CD or DVD – insert your disc, restart and hold down the C key.  Once the installer begins you can run Disk Utility (from the Utilties menu) or perform an Archive & Install.  Intel Macs can also boot from a USB flash drive which contains a bootable disk image, this can be very handy in an emergency.
You can also use a clone of your Mac hard drive to boot a cantankerous system.  This not only allows you to check, fix or copy data off the primary boot drive but continue working immediately when you have disk problems.  For more details see How (and Why) to Clone Your Mac Hard Drive.
More Tips and Suggestions?
I’m sure there are many other tips and suggestions on the topic of Mac startup problems; please let us know some of your ideas and experiences in the comments.