Saga continues. with the Drive removed normal access to Setup was resumed, so next step was to ensure that there was nothing lurking on a drive that would cause the problem, so I cleaned an SSD with Diskpart and reloaded Windows. Same problem. Out of curiosity I tried Hibernate instead of shutting down, that worked perfectly. Not only that, but the fault disappeared! So I proceeded to load some drivers, all fine until I installed IRST. Fault re-appeared, and was corrected by choosing Hibernate just once. Puzzled...
Regards,
Rex Long