Went to update an iMac (12,1) running OS10.6.8. Several minutes into the update, I forgot (don’t remember seeing the option) to do a clean install. I wanted all the old stuff gone so I cancelled the install. When that didn’t happen right away, I did a hard shut down of the computer by holding down the power button. Upon reboot with the 10.8 Mountain Lion disc, the computer keep beeping a slow pattern of three beeps.
I tried to reboot again. No change.
I tried to reboot with 10.7. No change.
I tried to reboot with 10.6. No change.
I tried to firewire target disc to another computer. That was successful. Went to install 10.8. That went fine for a while until the host computer started beeping the dreaded three beep pattern. I then went home for the weekend.
Thinking it might be a RAM issue, I exchanged the RAM. No change.
I ran Disk Warrior. Don’t know why I didn’t think to do this before. It ran successfully and rebuilt the directory. Then, I booted with the 10.6.8 disc. Three beeps.
I then found the original iMac OS X Install DVD (10.6.7). Aha. The computer liked it. System installed. System updated to 10.6.8. Ran update to 10.8. Success.