The Mac won't boot. Now what?

From...

by Larry Loeb

(IDG) -- If you run current Mac OS software, you can easily corrupt your system file badly enough to prevent startup. All it takes is a crash that forces you to reset by pushing the button on the front panel. If the System file is caught in an indeterminate state at the time of the crash, it won't be fully updated, and may contain invalid code which gets read on the next startup attempt. When that happens, the Mac gets confused and looks for a valid startup disk. If it finds none, the monitor will show a flashing question mark inside a folder icon. This is the point at which a user will usually call you and beg for help.

Your first step should be to check the hardware, which can fail or simply get corrupted. For example, a "wild write" by software can cause invalid data to be stored in the Mac's hardware Parameter RAM. The PRAM includes the data that determines which device the OS uses to start. Simply resetting the PRAM to default values can sometimes correct a boot problem. Resetting the PRAM is easy: hold down the Option, Command, P, and R keys at the same time while restarting the machine until the startup chimes sound. If the PRAM was the problem, the Mac will now boot normally and load the OS. You can then personalize the default PRAM values.

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Let's say that doesn't fix things. The flashing question mark is still there. Time to get out the Apple CD-ROM that contains the known good OS. Use the OS Installer CD-ROM, rather than the Software Restore CD-ROM you may also have. That one is for the non-System programs included with the Mac.

The OS installer disk is designed to make OS installation idiot-proof. Boot up using the CD-ROM drive (which may require you to press Command-C during restart) and see if the Mac recognizes its internal hard drive. If it doesn't, invoke Apple's Disk First Aid utility and see if "verify and repair" fixes things. Though the file structure of the disk may look fine with no repairs necessary, you still may not be able to boot. Nevertheless it's worth checking to see if the problem isn't just a munged disk directory.

If you're still stuck, the problem is probably in the System file itself. If the file won't open when you double-click it to reveal the font resources it contains, you can presume that diagnosis is correct. That means you must install new system software.

The CD-ROM makes the system file installation process easy; however, there is a nonobvious option that shows up about two screens past all the legalese at the beginning of the process. Click on the Options button and you'll be able to choose between "clean" and "inplace" installations. The former creates a new standard-issue System folder containing all the standard System software. The latter uses the existing System folder software and replaces only selected elements of it.

If there's a problem with one of the System software files, it's possible more may be corrupted, so I usually choose the clean installation and manually drag over the extensions and pref files I want to keep from the Previous System Folder the installer preserves.

If you are absolutely sure you know which software file is causing the problem, a customized inplace install may get you going again without the need to repersonalize the System.

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