Mac desktops forum: Mac won't boot at *all* - not even from CD/DVD

Yes, first eject the disk per the last reply. Beyond that, there could be many issues. Your hard drive may have been failing before you attempted the upgrade. I would attempt to boot from your original RESTORE disk for your machine and do a disk verify and repair on the Mac OS volume. If that passes, attempt to reboot again. If not, and the Snow Leopard update failed part way through, you may no longer have a bootable disk. At this point you are running out of o. I hope your data is backed up. You could try an archive install of the original OS, (i.e. from your RESTORE disk). Its probably your best chance at getting your system back.

One other altetnatives if you have no back ups is do what I did when I replaced my 9 year old G4 which would no longer boot (logic board, PMU issue.. drives were fine). I took the old drives out of the machine and bought an inexpensive drive enclosure and mounted the drives in them. I your case, buy a new drive for your Mac, replace the harddrive and take your old one and put in an enclosure. Don't attach external drive to your back yet. Do a clean install of Snow Leopard or your prior OS. Once the machine is up and running, you can plug your external enclosure containing your old drive into the USB/Firewire as appropriate and hopfully the OS will mount the drive. You can copy data off it as appropriate.

One of my computer maxims is to make sure a computer is fully operational and there are now known software or hardware issues before attempting an upgrade of OS. That applies to Mac OS X, Windows, Unix, and Linux.. any OS.

the reason that the ProSoft Data Rescue disk allowed the boot is because it contains a version of OS X unlike anything you have on your computer and that is what it used to boot the machine.

P