Problems with booting to Windows 10

[Japi]

I have problems with booting to Windows 10. When I choose the Windows partition from System Preferences / Startup Disk, the machine boots to a blank screen with a cursor blinking. But if I do a PRAM reset after that, the computer boots to Windows 10 and it works. Although I would assume the PRAM reset would always boot me back to Mac (not Windows side). If I hold the Option-key at startup, I can choose the Windows partition and it will boot there normally. Although I wouldn’t want to use this method, as I have a newer GPU that doesn’t support boot screen, so I can’t use that method with that GPU (I don’t want use the old Radeon 5770 GPU and would want to move to a newer GPU). So for that reason I would want to get the System Preferences / Startup Disk method working.

I found some suggestion from google about booting to Windows 10 installer CD and then running Bootrec.exe with /FixMbr, /FixBoot or /RebuildBcd, but for some reason it can’t recognize the the Bootrec-command, I don’t know if the installer can’t find the Windows partition for some reason.

The Windows 10 has been installed in EFI mode. And the computer is Mac Pro 5,1 with High Sierra 10.13.4 with MP51.0085.B00 bootrom with NVME injection (so I’m booting from a Samsung 970 EVO M.2 SSD and both High Sierra and Windows are in the same disk). From Windows 10 I can boot normally to Mac, choosing the Mac partition from the Bootcamp panel.

 

[tsialex]

1) Update your BootROM to 140.0.0.0.0, has native support for NVMe blades
2) Don't use Windows UEFI, install via BootCamp/CSM, then install the iMac Pro BootCamp. After that you can go from Mac to Windows and from Windows to the macOS.

Read here:

How to: Boot Camp without a Boot Screen

 

[Japi]

Thanks. So is it due to the UEFI mode of Windows that the High Sierra can't boot to the Windows side? Or it can't be fixed in anyway? Only by reinstalling of the Windows in Legacy mode? (As I can boot from Windows back to High Sierra normally without any problems, so only from Mac to Windows seems to be the problem for me)

 

[thornslack]

EFI install usually places itself as boot priority one which is why a pram reset is still landing you in windows. You can use easyuefi to set OS X to priority one or switch between os’s if need be. Start up disc in OS X seems unable to properly boot efi win 10 in my experience. Try bootchamp.