iMac Mid 2010 21.5" - OS Reinstall Issue

[garysauctions]

Acquired this used for a child to use for school.
Booted up and there is way too much garbage on here.
The seller said it had been gone over and 'redone' but it looks like instead of a reinstall they did something else.

I tried to boot off of a USB installer but got messages about the OS on the computer was newer than the boot drive.

What is on there right now? Mac OS High Sierra 10.13.6

I have a 10.14.x installer but it boots to the O/ icon saying " no can do "

What would be the easiest way for me to clear off this machine and reinstall an OS?

Would the " Select Network " option be viable and go from there, or will that try to revert to the original OS that came on the machine leading me to that " OS on the system is newer " deal.

I should know how to do this as I have done it frequently years ago, but I guess it was too many years.

ALL HELP APPRECIATED !!!!

 

[chscag]

The highest version of macOS that machine can run is High Sierra 10.13.6. Before you clear off that machine, make sure you first have a backup. I recommend making a bootable backup clone using Carbon Copy Cloner. Also make sure you can download a copy of High Sierra and use it to make a flash drive installer.

How to create a bootable USB masOS installer

Make a macOS installer with createinstallmedia and install Monterey or another macOS on multiple Macs, do a clean install, or access a faulty Mac.

www.macworld.com

Then boot to Recovery: (command plus R) enter utilities, Disk Utility, and erase the hard drive. After doing that, you should be able to use the High Sierra installer you made to boot the machine and install a fresh copy of High Sierra.

If anything goes wrong, use the bootable clone you made with Carbon Copy Cloner to get you back where you were before.

 

[garysauctions]

The highest version of macOS that machine can run is High Sierra 10.13.6. Before you clear off that machine, make sure you first have a backup. I recommend making a bootable backup clone using Carbon Copy Cloner. Also make sure you can download a copy of High Sierra and use it to make a flash drive installer.

How to create a bootable USB masOS installer

Make a macOS installer with createinstallmedia and install Monterey or another macOS on multiple Macs, do a clean install, or access a faulty Mac.

www.macworld.com

Then boot to Recovery: (command plus R) enter utilities, Disk Utility, and erase the hard drive. After doing that, you should be able to use the High Sierra installer you made to boot the machine and install a fresh copy of High Sierra.

If anything goes wrong, use the bootable clone you made with Carbon Copy Cloner to get you back where you were before.

Thank you --- I think we have a handle on it now.
I found an external bootable drive that mu son ran the 2007 24" from.
Hooked that up to this 21.5" and it booted and runs like a charm so that give me the freedom to go after the internal with full energy. LOL

I have a collection of bootable USB installer including this High SIERRA

Now I have something to do while on quarantine! LOL