I fixed the iMac

https://www.macworld.com/article/3092900/macs/how-to-create-a-bootable-macos-sierra-installer-drive.html


https://www.macworld.com/article/3204672/macs/how-to-create-a-bootable-macos-high-sierra-installer-drive.html


https://macdaddy.io/install-disk-creator/


http://www.idownloadblog.com/2015/09/14/how-to-start-up-mac-from-bootable-media/
















https://www.macworld.com/article/3092900/macs/how-to-create-a-bootable-macos-sierra-installer-drive.html




https://discussions.apple.com/thread/7485850


https://support.apple.com/en-gb/ht204904


https://macdaddy.io/install-disk-creator/


https://www.macworld.com/article/3204672/macs/how-to-create-a-bootable-macos-high-sierra-installer-drive.html