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MP 1,1-5,1 Mac Pro 5,1 not booting any OCLP USB anymore — stuck booting Mojave

Are there any drives in the SATA bays?
Is your cheepo MS mouse connected directly to your Mac Pro, or through the keyboard? (if the mouse is USB1, it would be a problem during OS install. Your keyboard is USB2, so chaining through the keyboard solves the problem.)
What drive is OpenCore EFI folder installed to?
What is the firmware version on your Mac Pro? System Profiler -> Hardware Overview: System Firmware Version (OCLP may obscure this - boot Mojave directly to see the real version. v 144.0.0.0.0 preferred.)

I've had better luck installing OCLP to the EFI folder of a SATA drive. I had boot problems putting OC directly on the NVME drive. If your firmware is an old version, you won't be able to boot from NVME until after OC loads - OCLP can supply NVME boot capability. But OC still has to boot first from a supported drive.

Is your RX580 flashed with Mac firmware? Without that, the firmware boot picker won't load. Blank screens with direct boot until late in the macOS boot sequence. OC supplies its own drivers, the OC boot picker can load, and provide full macOS boot screens afterwards.

If your RX580 has Mac firmware, then the boot picker may be failing due to a PCIe card being incompatible. Try pulling one at a time, until the boot picker reappears. For example, my Sonnet McFiver card prevents the firmware boot picker from loading.

A failing SATA drive (including an optical drive) can muck up booting or boot picker. Suggest unplugging your optical drive(s) for testing purposes.
 
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No drives in SATA bays
Yes, mouse is attached to the keyboard
DVD Drive disconnected

Firmware version 9999.9999.9999.9999.9999.
What?????

Something's obviously badly out of whack here
I have no idea what to make of this.

Screenshot 2025-11-01 at 17.48.33.png
 
Thing is I've still got the original USB Monterey installer I used to install on all 3 machines. This installer still works fine on the other 2 machines. By that I mean if you insert it one of the USB slots at the front then reboot while holding OPT it begins the Opencore install as normal. Obviously I didn't continue with that but the point is if I do the same on this machine the screen remains black forcing a hard reset. This is a machine stripped down to the bare bones i.e. RX580 and the system drive (SATA SSD). I also tried putting an empty Hard Disk in the mix just incase the installer required a possible target disk but it made no difference.
tsialex said:
You still need to boot anything between 10.6 to 10.14, native/without OC/OCLP, and check the real BootROM version.

If your Mac Pro doesn't have 144.0.0.0.0 yet, you will need to upgrade it.
Click to expand...
I've still got a High Sierra install on HD in a disk tray so it should be easy to get that info. I'll do that in the morning.
I appreciate your help.
 
It sounds like the RX580 in the one machine isn't flashed for Mac. Hence no firmware boot picker. You may have to swap in a different graphics card to get the boot picker back. Just long enough for the macOS install. Once you're all patched up with the OS version you want, you can go back to the existing RX580.
 
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