- Oct 6, 2015
- Asus Z97M-Plus
- i7 4790K
- Asus GTX 950 Strix
- Classic Mac
- Mobile Phone
This is because of Secure Boot is Enabled on BIOS.
Disable it and check.
Thanks for your help everyone.
I got everything up an running again yesterday. It seems that connecting the old iMac HD gave something a kick in the right place.
Can Secure Boot be enabled without entering BIOS? I've not been in there (or made any changes anywhere) since changing fan speed settings at least 6 months ago.
In addition, while iTunes and Safari updated on the 10/12/2016, the update to Sierra never actually happened. Having to update Nvidia drivers late yesterday also led me to believe the update had occurred on the same date.
After the huge fright this has given me I'm not sure that I want to try again.