10.5.8 Both hard drives OK, tested - will not boot past startup screen

Your hard drives may be OK, but the installed systems are not. You need to reinstall OS X on your startup volume. Doing this with Leopard requires your Leopard DVD:

How to Perform an Archive and Install

An Archive and Install will NOT erase your hard drive, but you must have sufficient free space for a second OS X installation which could be from 3-9 GBs depending upon the version of OS X and selected installation options. The free space requirement is over and above normal free space requirements which should be at least 6-10 GBs. Read all the linked references carefully before proceeding.

1. Be sure to use Disk Utility first to repair the disk before performing the Archive and Install.

Repairing the Hard Drive and Permissions

Boot from your OS X Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Installer menu (Utilities menu for Tiger, Leopard or Snow Leopard.) After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the installer. Now restart normally.

If DU reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.

2. Do not proceed with an Archive and Install if DU reports errors it cannot fix. In that case use Disk Warrior and/or TechTool Pro to repair the hard drive. If neither can repair the drive, then you will have to erase the drive and reinstall from scratch.

3. Boot from your OS X Installer disc. After the installer loads select your language and click on the Continue button. When you reach the screen to select a destination drive click once on the destination drive then click on the Option button. Select the Archive and Install option. You have an option to preserve users and network preferences. Only select this option if you are sure you have no corrupted files in your user accounts. Otherwise leave this option unchecked. Click on the OK button and continue with the OS X Installation.

4. Upon completion of the Archive and Install you will have a Previous System Folder in the root directory. You should retain the PSF until you are sure you do not need to manually transfer any items from the PSF to your newly installed system.

5. After moving any items you want to keep from the PSF you should delete it. You can back it up if you prefer, but you must delete it from the hard drive.

6. You can now download a Combo Updater directly from Apple's download site to update your new system to the desired version as well as install any security or other updates. You can also do this using Software Update.

If you made changes to permissions on the entire drive, then you would prevent the installed system from operating properly. This would require completely reinstalling OS X or doing the Archive and Install. The latter is the only non-destructive way of reinstalling Leopard. It's much simple with Snow Leopard and later. Have you tried this:

Repair the Hard Drive and Permissions

Boot from your Leopard Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the installer.

If DU reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.

Do me a favor. First, select the Desktop icon of your 10.6.8 drive. Press COMMAND-I to open the Get Info window. Expand the Sharing and Permissions panel at the bottom. Take a snapshot of what's displayed. Second, open Disk Utility, select this drive in the DU sidebar list, click on the Partition tab in DU's main window. Take a snapshot of this. Post them here. To snapshot just a portion of the screen press COMMAND-SHIFT-4. Use the crosshairs to select the desired portion of the screen. When you release the mouse button the image will be saved to your Desktop.

User the Camera icon you will see in the forum message editor's window's toolbar to post each of the snapshots you took.

Do you have a Snow Leopard DVD? If so, can you boot the computer with it? If so, then reinstall Snow Leopard on your original disk with Snow Leopard on it.

Reinstall OS X without erasing the drive

1. Repair the Hard Drive and Permissions

Boot from your Snow Leopard Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the installer.

If DU reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.

2. Reinstall Snow Leopard

If the drive is OK then quit DU and return to the installer. Proceed with reinstalling OS X. Note that the Snow Leopard installer will not erase your drive or disturb your files. After installing a fresh copy of OS X the installer will move your Home folder, third-party applications, support items, and network preferences into the newly installed system.

Download and install Mac OS X 10.6.8 Update Combo v1.1.

No, it will not disturb your files. When it is completed you will want to Download and install Mac OS X 10.6.8 Update Combo v1.1. This will return it to 10.6.8. Use Software Update to check for any other updates you may need to reinstall.

And, you did the first part - repaired the hard drive and permissions before installing?

It sounds like you ran out of disk space. Your drive doesn't have sufficient free space on it.

Freeing Up Space on The Hard Drive

1. See Lion/Mountain Lion's Storage Display.

2. You can remove data from your Home folder except for the /Home/Library/ folder.

3. Visit The XLab FAQs and read the FAQ on freeing up space on your hard drive.

4. Also see Freeing space on your Mac OS X startup disk.

5. See Where did my Disk Space go?.

6. See The Storage Display.

You must Empty the Trash in order to recover the space they occupied on the hard drive.

You should consider replacing the drive with a larger one. Check out OWC for drives, tutorials, and toolkits.

Try using OmniDiskSweeper 1.8 or GrandPerspective to search your drive for large files and where they are located.

The reinstallation may have failed because of the permissions problem or you may have tried installing Snow Leopard on your Leopard drive instead of the one that already has Snow Leopard installed. What happened when it failed to repair permissions? What error message?

There's a limit as to what one can do with little free disk space to work with, and not knowing exactly what the problem is with the drive.