im in the process of downgrading from os Mojave to os High Sierra, but when i restart and hold the option key it won't bring up the start up manager. it just either boots to home screen or the tower turns on but does not turn on my screens. ive tried downloading Boot Manager but when i select the USB with High Sierrs on it it just reboots to home screen. Any help would be amazing
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MP 1,1-5,1 [Solved]Need some help downgrading from Mojave to High Sierra
- Thread starter tuneman97
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If you have a non-Mac EFI GPU that works with High Sierra, NAVI and VII won't, you have to make an USB installer of High Sierra, shutdown, remove all disks from your Mac Pro, install a brand new (or previously erased disk), connect the createinstallmedia USB key, then power on and do a 3-times sequentially clear NVRAM.
After around 3 or 4 minutes, your Mac Pro will have fully loaded the macOS installer from the createinstallmedia USB key and the display will work. When you don't have any SATA/PCIe/Firewire bootable disks, the next one to be loaded is the USB bootable ones, this is valid for Apple or PC GPUs.
After the macOS installer is loaded and you have a working display, you just need to format de disk and complete the install.
Good luck.
This worked! I can’t thank you enough man this has been a serious mind bender for me. Your the best