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That doesn’t make sense because I didn’t attempt any windows install once on Mojave, just reset the NVRAM and it hasn’t been turning on since. If I can get this to boot finally I’m just going back to High Sierra just too many issues

Okay, well I wasn’t sure. It sounded like you were getting Windows screens from a mac only drive connected. Im not sure how thats possible.

If your macOS install isn’t borked, it should boot in a drive bay. Otherwise, it sounds like you need to reinstall or restore a backup.
 
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Yes. It's very easy to make one. You need an 8GB or larger USB drive. This page has two different methods you can follow.

Once you make the USB installer then plug it into your cMP and boot up holding the "c" key on the keyboard. You will need your Vega installed. Do not install the GT-120. There will be a black screen for several minutes, but eventually the installer should load up Follow the steps to install macOS on your existing partition.

If you have critical files on your macOS drive that you don't have backed up, then you may want to connect that drive to another computer first to try to copy over the files you care about, just in case. Re-installing macOS is supposed to preserve everything but if your partition scheme is screwed up it may be necessary to wipe the existing partitions to get macOS to install.

Edit: If you're willing to go back to High Sierra then make a High Sierra USB installer via similar steps. Then you can just use your GT-120 and have the benefit of seeing everything that's going on.
Tried your suggestion and nothing with the Vega 56, it chimes and the screen remains black then just shuts down. I really don’t know what else would be causing it not boot at all, I’ll try using the GT120 instead to see if this makes a difference.
 
Thank you so much man, this didn’t work either unfortunately. I’ll try doing the recovery mode method next. I thought you needed an EFI GPU in order to get to recovery mode? Or am I just incorrect?

You don't need any Mac EFI GPU to access recovery partition. All you need is just a OOTB supported GPU, Vega is one of them (if your recovery partition is up to date).
 
It looks like you must have done a Windows repair at some point with both drives connected (OSX and Windows), which screwed the EFI partition. Windows tends to do that. it's bootloader normally hijacks the osx boot loader.
 
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Yes. It's very easy to make one. You need an 8GB or larger USB drive. This page has two different methods you can follow.

Once you make the USB installer then plug it into your cMP and boot up holding the "c" key on the keyboard. You will need your Vega installed. Do not install the GT-120. There will be a black screen for several minutes, but eventually the installer should load up Follow the steps to install macOS on your existing partition.

If you have critical files on your macOS drive that you don't have backed up, then you may want to connect that drive to another computer first to try to copy over the files you care about, just in case. Re-installing macOS is supposed to preserve everything but if your partition scheme is screwed up it may be necessary to wipe the existing partitions to get macOS to install.

Edit: If you're willing to go back to High Sierra then make a High Sierra USB installer via similar steps. Then you can just use your GT-120 and have the benefit of seeing everything that's going on.

Thank you again for your help, it's been a bit since I last tried this. I tried doing everything you said with a Mojave USB an it still won't fully power on. I then decided to try again but with a high sierra one and used the GT120. The result was an extended grey screen followed by the strange windows screen. Could the windows issue be related to the GT120? I know to get Mojave it installs new firmware and everything, I'm not sure what else would cause that whole issue without any other windows partition not installed. Could trying a different graphics card work possibly?
[doublepost=1541445454][/doublepost]
It looks like you must have done a Windows repair at some point with both drives connected (OSX and Windows), which screwed the EFI partition. Windows tends to do that. it's bootloader normally hijacks the osx boot loader.
any idea on how to fix this if this is the case?
 
Thank you again for your help, it's been a bit since I last tried this. I tried doing everything you said with a Mojave USB an it still won't fully power on. I then decided to try again but with a high sierra one and used the GT120. The result was an extended grey screen followed by the strange windows screen. Could the windows issue be related to the GT120? I know to get Mojave it installs new firmware and everything, I'm not sure what else would cause that whole issue without any other windows partition not installed. Could trying a different graphics card work possibly?
[doublepost=1541445454][/doublepost]
any idea on how to fix this if this is the case?

With the GT-120 installed and your High Sierra USB installer plugged in, power on the cMP and immediately upon hearing the boot chime, hold down the Option key on the keyboard until a gray screen shows up. If done properly icons for any bootable device should show up. If you made your USB installer drive correctly then you should see one for "Install macOS High Sierra" or something like that. Use the mouse to click on it (or arrow over on the keyboard and hit return).

That should eventually get you to the installer screen.
 
Thank you again for your help, it's been a bit since I last tried this. I tried doing everything you said with a Mojave USB an it still won't fully power on. I then decided to try again but with a high sierra one and used the GT120. The result was an extended grey screen followed by the strange windows screen. Could the windows issue be related to the GT120? I know to get Mojave it installs new firmware and everything, I'm not sure what else would cause that whole issue without any other windows partition not installed. Could trying a different graphics card work possibly?
[doublepost=1541445454][/doublepost]
any idea on how to fix this if this is the case?
If you can get to the EFI folder (it is hidden and it is FAT32) you can delete the Windows files from there and you should be OK to go, without reinstall
[doublepost=1541449811][/doublepost]You should try with ubuntu live cd or USB you might get access to that folder
 
Okay, I have some good news and it had to do with the multiple volumes for windows mentioned earlier. Thank you again to all of you for your help it really means a lot, I’ll explain it this way:

Trying to install windows on my other 250gb HDD must have been what caused these issues. I don’t know what happened for the repair volumes to be stored on my Mac OS 250gb SSD but it did, thankfully I store all of my video files and other data on my other external drives so I’m not going to lose much important information if any. So now I’m doing a clean instal of high Sierra for now and will think twice about doing Mojave, I’ll look more into some of the guides here on windows 10 as my whole story for how I tried installing it in the first place is a nightmare to begin with. So thank you, I’m definitely going to be going on here more for Mac Pro support and discusssions in the future :)
 
I have a similar situation, but a little different. MAC Pro built is similar, I just got a MSI RX580, worked OOTB, very exciting, upgraded to mojave, worked fine too, but windows won't boot. I was trying to follow h9826790's suggestion to do a DVD installation, since there is no boot screen if I use RX580, switched back to GT120, but there is no way to boot into C drive, very weird. The most interesting thing was, I accidentally booted into Mojave once, ON GT120!!! Then I decide to do a PRAM, but I only heard chime once, then the unit hung forever. I have to shut it down, since then the unit won't boot again, tried everything, no screen, no chime, fans runs, GPU fan runs too. And I found that it looks like there is no power on USB port, everyone of them, the led light of the mouse connected to USB port does not shine at all. I have no idea what happened, is that my motherboard got fried? Appreciate if any one can help me out.
 
I have a similar situation, but a little different. MAC Pro built is similar, I just got a MSI RX580, worked OOTB, very exciting, upgraded to mojave, worked fine too, but windows won't boot. I was trying to follow h9826790's suggestion to do a DVD installation, since there is no boot screen if I use RX580, switched back to GT120, but there is no way to boot into C drive, very weird. The most interesting thing was, I accidentally booted into Mojave once, ON GT120!!! Then I decide to do a PRAM, but I only heard chime once, then the unit hung forever. I have to shut it down, since then the unit won't boot again, tried everything, no screen, no chime, fans runs, GPU fan runs too. And I found that it looks like there is no power on USB port, everyone of them, the led light of the mouse connected to USB port does not shine at all. I have no idea what happened, is that my motherboard got fried? Appreciate if any one can help me out.

If the logic board dead right after PRAM reset.

And you can't boot into Windows (I assume that EFI mode installation).

It sounds very like the BootROM is corrupted.
 
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Why do people install Win10 on these boxes as bare metal? Why not just run a VM? Windows is rude. It hoses boot partitions and corrupts BootROMs.

VirtualBox is free.
 
Why do people install Win10 on these boxes as bare metal? Why not just run a VM? Windows is rude. It hoses boot partitions and corrupts BootROMs.

VirtualBox is free.

Because Client OS cannot use more hardware than the Host OS, which means, we can never get the real GPU power in VM Windows. e.g. Since macOS not allow us to use GPU hardware decode / encode, therefore, we can't use that in VM Windows as well.

And of course, no DirectX 12 support in VM Windows as well. Even DirectX 11 is only partially supported.

And VM cannot help to flash GPU, upgrade SSD firmware, run hardware test, etc.

VirtualBox is free, but super weak in utilising GPU power.

Windows only mess up BootROM in EFI mode, which Apple never ever said cMP is supported. Legacy Windows is 100% safe in this area.

It also won't mess up another partitions unless the user do it. It's the Apple bootcamp apps (macOS application) mess up the macOS partition, not Windows.

Native Windows legacy installation on a separated hard drive is 100% safe to macOS and cMP firmware. Which means, not Windows fault, but Apple (bootcamp)/ user (choose wrong installation mode or method) mess up something, not MS or Windows.
 
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Because Client OS cannot use more hardware than the Host OS, which means, we can never get the real GPU power in VM Windows. e.g. Since macOS not allow us to use GPU hardware decode / encode, therefore, we can't use that in VM Windows as well.

And of course, no DirectX 12 support in VM Windows as well. Even DirectX 11 is only partially supported.

And VM cannot help to flash GPU, upgrade SSD firmware, run hardware test, etc.

VirtualBox is free, but super weak in utilising GPU power.

Windows only mess up BootROM in EFI mode, which Apple never ever said cMP is supported. Legacy Windows is 100% safe in this area.

It also won't mess up another partitions unless the user do it. It's the Apple bootcamp apps (macOS application) mess up the macOS partition, not Windows.

Native Windows legacy installation on a separated hard drive is 100% safe to macOS and cMP firmware. Which means, not Windows fault, but Apple (bootcamp)/ user (choose wrong installation mode or method) mess up something, not MS or Windows.
Plus I have currently 3 Windows installations in EFI mode. Yesterday I also booted from a USB with Windows in EFI mode. All works perfect no Bootrom corruption. Alex mentioned specific scenario when switching from old bootroms to a new one. That scenario is long time in the past.
 
If the logic board dead right after PRAM reset.

And you can't boot into Windows (I assume that EFI mode installation).

It sounds very like the BootROM is corrupted.

Thanks h9826790, I will try anything to bring it back. Is there any guideline to repair the bootrom? My mac pro is 4.1 flashed to 5.1, and updated to Mojave, which version of bootrom I need to use? Appreciate your help.
 
Plus I have currently 3 Windows installations in EFI mode. Yesterday I also booted from a USB with Windows in EFI mode. All works perfect no Bootrom corruption. Alex mentioned specific scenario when switching from old bootroms to a new one. That scenario is long time in the past.

I just have a dedicated Windows box. I guess if cost or space is a real issue, do what you have to. You can build a Win PC that smokes any 2009-2012 MP for fairly cheap.
 
I just have a dedicated Windows box. I guess if cost or space is a real issue, do what you have to. You can build a Win PC that smokes any 2009-2012 MP for fairly cheap.
12 core CPU x5690 is on par with the current systems .It is single CPU where it lacks performance and all applications which require single CPU .The RAM can be faster too on newer systems .
 
12 core CPU x5690 is on par with the current systems .It is single CPU where it lacks performance and all applications which require single CPU .The RAM can be faster too on newer systems .

Trolling or serious? Can’t be serious.
 
Multicore performance of a dual Xeon X5690 Mac Pro is on par with current Macs, it's the single CPU score that isn't.

My comparison was between cMP and current PC given as the reason for not running Win on cMP. Upgraded cMP is on par with the trashcan, but not with an 8th/9th gen Intel CPU running something like DDR4-2666. There are some unrealistic scenarios with impossibly multithreaded apps where the cMP can keep up, but the other 99% of the time it’ll feel sluggish. I know because I have the two side by side and use both daily.
 
Thank you h9826790, there is tons of info. Since my cMP can't start, guess I have to use "firmware restoration CD" to restore bootrom first to get it started. The CD I found on Apple website was publish in 2010, for cMP 5,1, my question is if I use this rom, can Mojave be started? or I have to re-install some old version first? Thanks a lot!!!
There is a remote chance that you can restore your BootROM with the Firmware Restoration CD. Minimal.

If you are extremely lucky and it works, you can boot up to 10.12.6.
 
Thanks tsialex, since my cMP won't boot, what other option I have. Appreciate it!
You have to find what is your problem. A brick will power on everything but just won't progress from there, USB ports get power.
 
You have to find what is your problem. A brick will power on everything but just won't progress from there, USB ports get power.

OK, thanks tsialex, this will take some time for me to investigate. Thanks you and I will report her if I will find a way.
 
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