Snow Leopard cannot be installed on Macintosh HD the disk "cannot be used to start up your computer"

When trying to install Snow Leopard, some people are having a problem where the installer will not recognize the current boot drive as a valid destination for Snow Leopard. Instead, it will display the drive with a yellow triangle on it, indicating something is wrong with that drive. When the drive is selected, the installer claims the system cannot boot from the drive.

Apple discussion poster "redpola" writes:

"I closed all my apps. I ran the installer. I agreed to the terms. I am asked where to install Snow Leopard. Only one disk is available - my boot disk. It has a yellow triangle on it.

Selecting the disk tells me 'Mac OS X cannot be installed on Macintosh HD, because this disk cannot be used to start up your computer.' Rebooting and attempting an install direct from CD yields the same results."

This problem happens because the Snow Leopard installer detects a small discrepancy in the partition table of the drive, and assumes booting off the drive may not be successful. The fixes involve rewriting the table without formatting the drive, but if that does not work then formatting should definitely work (provided you have a backup).

Fixes:

1. Run drive checks.

The first thing to do is run Disk Utility or, even better, run a third-party utility program to check out the drive to ensure it is functioning correctly. Fixing any errors may require booting off a volume other than the boot volume (i.e., the Snow Leopard DVD or a Drive Genius DVD), and performing the fixes from there.

2. Repartition the drive.

This problem might happen even if the drive checks out with various disk utility software. The way around this is to have Disk Utility repartition the drive, which, luckily, can be done without having to format the drive. To do this, boot from the Snow Leopard DVD and select your language. Then launch "Disk Utility" from the "Utilities" menu and perform the following steps:

1. Select your boot device (the device above the boot volume name), and select the "Partition" tab.
2. Resize the partition by selecting the volume name in the rectangular volume representation and drag the bottom-right corner of it to change its size.
3. Click "Apply" to change the partition's size.
4. Revert the change by dragging the same resizing corner back to the bottom, and click "apply."

After this is done, quit out of Disk Utility and try installing Snow Leopard again. Since you are booted from the Snow Leopard DVD you should be able to continue immediately without having to reboot your system.

Workarounds:

1. Format and install.

If you have a full system backup via Time Machine or a drive clone, you can format your boot drive and do a clean install of OS X. To do this, first be sure your backups are complete and accessible, and then boot off the Snow Leopard DVD (click the "Utilities" button instead of "Continue" in the Leopard installer, or reboot and hold the "C" key to boot off the CD/DVD drive). When the installer loads, select your language and then launch "Disk Utility" from the "Utilities" menu and perform the following steps:

1. Select your boot device (the device above the boot volume name), and select the "Partition" tab.
2. Select "1 partition" from the drop-down menu, and then give the partition a name and format it as "Mac OS Extended (Journaled).
3. Click the "options" button and select "GUID" for the partition table.
4. Close this window and click "Apply" to repartition the table.
5. Close "Disk Utility" and continue with the Snow Leopard installation.
6. When the installation completes, migrate your data from your backup to the new system.

In this procedure, you can migrate from either your Time Machine backup, or from a cloned drive. Keep in mind that when you do this you may need to reinstall some programs since a clean install may break some application dependency links to system files.

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Topher has been an avid Mac user for the past 10-15 years, and has been a contributing author to MacFixIt for just over a year now. One of his diehard passions has been troubleshooting Mac problems and making the best use of Macs and Apple hardware both for family and friends, as well as in the workplace. He and the newly formed MacFixIt team are hoping to bring enhanced and more personable content to our readers, and keep the MacFixIt community going here at CNET. If you have questions or comments for Topher or the other MacFixIt editors, feel free to contact us at http://www.macfixit.com/contact

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