MP 7,1 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.