Hello Kurt, it seems you have helped and replied to many posts on here. I know you are probably sick and tired of hearing this...I'm having same issues as many people that posted here.
I received iMac from a friend (model a1224). It had Version 10.7.5 and I wanted to reboot/restart it. I followed the steps that I found on Apple site and I came to same problems as many people did here.
Link- https://support.apple.com/en-us/HT204904
I started by turning on the computer and holding option+command+r. The Mac OS Utilties window came up. So I selected Disk Utilities, went to my Macintosh HD drive (I wasn't sure which one I should have erased)...erased it...(probably selected the wrong harddrive, after reading all these posts). After erasing it, the drive was unmounted. So I mounted it back and returned to Utilities page and tried installing the OS. I have Gone to the step where you select a drive to install the os on(I'm using a phone to type this...when I get on my laptop I will send pictures). I select the macintosh HD and click install and come to the point where it asks for Apple ID. I first entered my own Apple ID, it says "this item is temporarily unavailable" try again later. So with that problem...I started to search for more posts on line.
I went back to Disk Utilities and selected the first hard drive listed which is Hitachi HdT7.... and went to erase it. So it turned out it tried to erase the Macintosh HD drive but a message came up "Disk erase fails, couldn't unmount Disk."
So my next step was to go into "partition". I select partition 1, the guid partition table is selected, format setting is Mac OS extended (journaled) and I make up a name and I click apply... and I receive a message. "Partition failed, couldn't unmount Disk".
I think I have tried everything....at this point the Mac OS X utilities starts up without even using command option R.
I have also tried getting my friend's Apple ID to log in during installing the OS and it still ends with the same error. "This item is temporarily unavailable"
Do you think I might be able to "rescue" the computer so I can use it?
I was also wondering if there's any way to transfer ownership of the computer from one ID to another. For example, deactivate it on my friend's account and activate it under mine and maybe that will work and let me log in and install it. (Just an idea)