Resolved 7,1 Bootcamp issue Win11/Macos26 Screen goes black 10s after MAC login

[Varmann]

I have a MacPro 7,1 with MPX Radeon 580x
I intend to use it mainly for Windows, but also as a Mac backup.

I installed Tahoe 26.4, it went nice. Rebooted a couple of times and removed most of the glassy features of OS 26.
I then went through the hopes to install Win11. It also went ok.

I set bootcamp to start as win.
All fine, I removed a lot of Win bloat. I restarted the win disk a couple of times. My plan was to upgrade Win with a Radeon 9070.

Issues came when I then started with option key and chose the Macdisk.
Login screen came up. I logged in. Progress bar started to move but after 10s the screen went blank. Restarted a couple of times with same result.

I then booted up in Windows with the option key. Changed the boot disk to mac and tried once o more.
Same result, but after that the option key OS-select does not come up. It boots to Macos and I get a black screen 10s after login.

How do I get out of this mess, since I now have now working OS.
I am very grateful for suggestions

Edit: Cmd+r does not work either. I have usb wired keyboard and mouse + Ethernet cable. MPX card is connected with HDMI.

 

[reader50]

Try a different monitor. If your monitor is failing, or doesn't like the HDMI handshake from your Mac, then you get black screens after a few seconds. And after repeated forced shutdowns, your Mac will be trying to safe-boot. Option-boot and recovery might even be working, but you don't see it because the screen stays dead.

 

[Varmann]

Thanks, it seemed to be a handshake issue.

It affected both the Mac volume and a bootable Tahoe install USB. Not directly but after the progressbar had start to advance. I use a 48" Asus display.

Using another display (LG 41") macos came up normally. Both using HDMI.

Using Option-key to switch boot volume is still tricky.
From MacOS:
Some places says, you have to press it while power on and release when the disk images shows up.
That do not work, it goes directly to Mac login.
If I wait to press option until the Apple symbol shows up. I will get access to startup volumes. Nice to discover that

During a windows boot I cannot get access to startup to the startup volumes, maybe I have not figured out the trick.

Edit: switching HDMI connector solved the handshake problem on my 48" display.

 

[mattspace]

Thanks, it seemed to be a handshake issue.

It affected both the Mac volume and a bootable Tahoe install USB. Not directly but after the progressbar had start to advance. I use a 48" Asus display.

Using another display (LG 41") macos came up normally. Both using HDMI.

Using Option-key to switch boot volume is still tricky.
From MacOS:
Some places says, you have to press it while power on and release when the disk images shows up.
That do not work, it goes directly to Mac login.
If I wait to press option until the Apple symbol shows up. I will get access to startup volumes. Nice to discover that

During a windows boot I cannot get access to startup to the startup volumes, maybe I have not figured out the trick.

Edit: switching HDMI connector solved the handshake problem on my 48" display.

Can you use the startup disk prefpane (and if there's a windows equivalent of it), rather than the boot time option selector and get a different result?

 

[reader50]

If your HDMI monitor is fussy about handshake with your graphics card, try an active display adapter (Displayport to HDMI). The adapter will have the latest HDCP version, which I suspect is the failure cause. I've used this trick on several fussy HDMI TVs used as monitors.

 

[mattspace]

If your HDMI monitor is fussy about handshake with your graphics card, try an active display adapter (Displayport to HDMI). The adapter will have the latest HDCP version, which I suspect is the failure cause. I've used this trick on several fussy HDMI TVs used as monitors.

The problem they have is the card only has HDMI ports, and the only DP output option will be from one of the IO card or top case TB ports, which their Win 11 may not have drivers to enable.

 

[Varmann]

After a month, it works like a dream as a win11 game machine. I bought it refurbished at a little over $2000, I gladly paid extra for the beauty and craftsmanship of it. Together with the radeon 9070 it is whisper quiet. Not as fast as a PC with 5090, but enough for me, and it cost way less than a single 5090 card in my country. I also have a decent Mac-backup should my Studio fail.