The scenario is a machine has had its hard drive replaced with a windows Operating System. On the boot menu you don’t get the option to boot to a USB or the recovery software from the Internet option.
Tools needed:
- Thunderbolt 2 , 3 lead and firmware 800 with adapters for thunderbolt 2
- USB boot operating system relevant to the age of the Mac.
- Test Machine to connect Target Disk Mode.
So the way to get round this is target disk mode the Mac (always a good plan) press down the T key when the Mac boots. You should see very quickly the Target Disc mode icon which is the logo for Fireware 800 and Thunderbolt. (see top photo) Plug in the thunderbolt/ firmware 800 cable cable to the machine with the issue and the test machine that will see the hard drive. On the Test Machine you should see the drive show up in the desktop as an external drive. In Disk utility locate the external drive drive and format the drive. Make sure you get the root drive, in disk utility you have the option to show all devices which will help with this task. Format option either APFS (Apple File System) or Mac OS Extended (Journaled) my recommendation as the drive will be formatted to APFS if required when you install the Operating System.
Once done eject the drive and hsut down the Target disk mode Mac. Unplug the Thunderbolt/Firefire 800 cable at both ends. Plug in your USB Operating System and boot the Mac that had the issue making sure when it boots you press the alt key to get the boot sequence options.
Select the USB drive and wait for it to boot into the Operating System installer and follow the online screen to install the clean Operating System to the drive you formatted earlier.
Once the installer is completed eject the USB installer and reboot the Mac. You should now ahem a clean system that you can work with.
Fault checking:
If the machine does not boot or the Operating System fails it might be a hardware issue. A easy way to test this is boot to a clean system from a USB boot Operating System. If that works then it’s a high probability it’s an issue with the drive. If it does not boot then the Graphics card is the logical concussion.