Your system’s firmware is not the correct one for your systems installed OS. You now likely have no OS on the drive now but still have the wrong format on it.
Your system likely had MacOS Sierra or something older and you installed either High Sierra or Mojave onto the drive but for some reason didn’t update the systems firmware so it can’t recognize the newer APFS file system the drive now has on it (Sierra and older MacOS uses HFS+)
The easiest way to fix this is to leverage your dads system to format and then prep the needed USB drive to install the correct OS onto your system.
First is your dad’s Mac running Sierra? If it is then we can move forward.
If not you’ll need to see if you can get ahold of the Sierra OS installer so you can create a bootable USB system to startup your system and you want to copy over the OS installer to it as well. Then you can use it to prep your system. Unlike a bootable OS installer we need a full OS installed onto the drive. Make sure you formatted the USB drive with GUID and a journaled file system!
But, we still have a problem! As the your systems drive is still not formatted to the needed HFS+ file system. Here we’ll leverage your dads system using Target Disk Mode and connecting your system to his via a Thunderbolt cable. Here’s how [https://support.apple.com/en-us/HT201462|Use target disk mode to move files to another computer].
Here we want to format your systems drive with a fresh GUID format and setup using a journaled file system (HFS+). That way we are back to the correct format for your system to use.
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Next we want to reboot your system with the Sierra USB drive we’ve created. Still have one hiccup here! You’ll likely need to use the Option Key to gain access to the Startup manager to select the USB drive as the startup disk. Now we should be able to run the OS installer! - '''DONE!'''
+
Next we want to reboot your system with the Sierra USB drive we’ve created. Still have one hiccup here! You’ll likely need to use the '''Option (⌥)''' key to gain access to the Startup manager to select the USB drive as the startup disk. Now we should be able to run the OS installer! - '''DONE!'''
Your system’s firmware is not the correct one for your systems installed OS. You now likely have no OS on the drive now but still have the wrong format on it.
Your system likely had MacOS Sierra or something older and you installed either High Sierra or Mojave onto the drive but for some reason didn’t update the systems firmware so it can’t recognize the newer APFS file system the drive now has on it (Sierra and older MacOS uses HFS+)
The easiest way to fix this is to leverage your dads system to format and then prep the needed USB drive to install the correct OS onto your system.
First is your dad’s Mac running Sierra? If it is then we can move forward.
If not you’ll need to see if you can get ahold of the Sierra OS installer so you can create a bootable USB system to startup your system and you want to copy over the OS installer to it as well. Then you can use it to prep your system. Unlike a bootable OS installer we need a full OS installed onto the drive. Make sure you formatted the USB drive with GUID and a journaled file system!
But, we still have a problem! As the your systems drive is still not formatted to the needed HFS+ file system. Here we’ll leverage your dads system using Target Disk Mode and connecting your system to his via a Thunderbolt cable. Here’s how [https://support.apple.com/en-us/HT201462|Use target disk mode to move files to another computer].
Here we want to format your systems drive with a fresh GUID format and setup using a journaled file system (HFS+). That way we are back to the correct format for your system to use.
Next we want to reboot your system with the Sierra USB drive we’ve created. Still have one hiccup here! You’ll likely need to use the Option Key to gain access to the Startup manager to select the USB drive as the startup disk. Now we should be able to run the OS installer! - '''DONE!'''