You went through all the steps in this Apple note except the steps to repair the hard drive or reload the system? Repairing the hard drive is one of the more important recovery steps.
You have no bootable backup?
Have you called Apple support to see if they still have the original OS X disks for your system? Do you know anyone with OS X 10.5 Leopard operating system disks?
The last step in that Apple note above is to make an appointment at the Genius Bar in an Apple store.