RMA was accepted (says they tested it and so I assume they found fault) - now to decide whether to get a GTX 1650 Super instead! (Having read about lots of issues people have with Radeon drivers and RX5x00 cards...)
The monitor worked fine through the card even in Windows before the driver was installed. I just assume that without a driver (other than default Windows) much of the GPU hardware isn’t used.
Thanks for the various suggestions. None address the issue of why this was working before and now does not. I do wonder if the GPU may developed have a fault.
Here's the latest - I tried once more to install the Radeon drivers having uninstalled my AV (BitDefender) ... and the PC hangs as...
This problem started happening about a week ago - before all was fine with my system, running 20.4.2 and then 20.7.1 of Adrenaline.
Here's what happens - during startup (BIOS logo disabled) the windows "logo" appears (the blue parallelogram) with the cycling dots - this then stops and the top...