Mac OS X: Troubleshooting the Mac OS X Installer

First, try general troubleshooting

This document focuses on Installer-specific aspects of installation troubleshooting. For more general advice, see "Mac OS X: Troubleshooting Installation and Software Updates".
Can you "mount" the disk image?

Mac OS X software updates downloaded from Apple's Web site are in the form of a .dmg files. For information on troubleshooting decoding downloaded software, see "Software Downloads: Software Formats and Assistance".

Is the download finished?

Downloading an entire software update on a slow Internet connection can take some time. Depending on how you download a .dmg file, it might display in the Finder despite being incomplete. The Mac OS X version of Disk Copy makes .dmg files appear on your desktop or in a Finder window as a disk. Disk Copy checks the integrity of the .dmg file. If the disk image appears in the Finder as a disk, then the download is complete.

Unexpectedly Quit?

If an alert box appears with this message: " The Installer Unexpectedly Quit," with or without a specific error number, try reinstalling.

Tip: Installing Mac OS X 10.1 or later without erasing previous versions should be more reliable than upgrading from or reinstalling 10.0. through 10.0.4 versions of Mac OS X.

Disk does not appear in Installer

If the Installer does not display the desired disk or volume, see "Installer Does Not Display Hard Disk".

Disk appears dimmed ("gray")

If the desired volume appears dimmed in the Installer, see "Disk Appears Dimmed (or "Grayed Out") in the Installer".