After selling my 2017 i5 iMac to a woman from Scottsburg and setting up my 2020 iMac, I needed to prepare my recently purchased 2017 iMac (with an i7-7700K) for resale.
The first step was to remove the Windows partition and erase everything on the computer — and that's where the problems began.
I used Boot Camp to remove the Windows partition I had previously created, which should have reclaimed the 1.6 TB I had allocated to Windows. While the program successfully deleted the partition, it reported an error when attempting to reclaim the storage space. I then tried using Disk Utility (the Mac partition tool), which also failed and told me to try running it from Recovery Mode, which didn't work. A few years ago, I tried the same thing on my old, dying 2009 iMac, and that attempt had failed too.
Newer iMacs have a built-in feature to securely erase everything automatically, but while the option exists in macOS, it doesn't actually function on older models. So, the recommended method is to boot into Recovery Mode, reformat the drive, and reinstall the OS — a process I had successfully completed on the iMac I just sold.
Unfortunately, the 2017 iMac with the i7 processor reformatted the drive but threw an error during the OS installation. It simply refuses to install. At this point, I have a $400 paperweight with no operating system.
I'm starting to wonder if the 2 TB hard drive might be defective. It is, after all, an eight-year-old computer.
Next, I'll try creating a bootable USB flash drive with the macOS installer using my 2020 iMac. According to everything I've read online, that's the recommended next step if the OS won't install through Recovery Mode. It is probably what the repair shop would try.