Windows 10 suddenly doesn't boot up any more on my iMac

Hi there,

For a number of years I have been using an old 27" iMac (12,2) with a 1TB SSD to run various versions of Windows that over time I upgraded (7 and then to 10) via Bootcamp that also has Mavericks installed on it (10.9.5) which I rarely boot into these days. Currently it has Windows 10 10 20H2 installed on it and in general this version of Windows 10 has been working fine.

Today I had a bit of an issue with Windows 10 where I had to reboot it, but it was taking some time to restart so I powered off and then restarted (which I know I shouldn't have but I got a bit impatient!), but after the chime it black screened on me without it showing a flashing cursor or Windows logo.

After a few reboot attempts I decided to try a PRAM reset but just could not get past the black screen, so I then alt booted to bring up the boot menu and was able to boot into the Mavericks partition and from there I can see and read the Windows partition fine via Tuxera.

I've tried some more PRAM resets to no avail and now if I don't choose the alt boot to bring up the boot menu, it will either white screen if the startup disk is set to Mavericks when rebooting from Mavericks, or if I select to boot to Windows as the start up or via the boot menu then it will show the Win logo but just with the spinner going constantly. After a few reboots it would say it's starting the Automatic repair with the same logo and spinner but during that process it will then eventually blue screen with a DRIVER_PNP_WATCHDOG error, then reboot back to the same Win logo.

I also tried to use the Windows media creation tool to create a bootable USB to try and run a repair but this shows the Win logo and then a few minutes later the same DRIVER error and then reboot and repeat.

Thinking that maybe the latest release of Win 10 might be an issue, I also tried to create a USB bootable using an earlier ISO release of Windows 10 from May 2020 using Rufus but although this USB appeared in the boot menu, selecting it caused the iMac to freeze on the boot menu.

Would anyone have any ideas as to what to try next as I'm going round in circles trying to get Windows 10 to boot again?