OK, I’m half happy. After spending a lot of time googling and trying things to clean my system, I finally did a complete reset of Windows 10 (a real pain as there are a lot of apps I’m going to have to reinstall).
After the reset I’ve been able to install odrive with no problems, so that’s a real plus. Tony, thanks for your help.
The only (extremely frustrating) downside is that when I run sfc /scannow I still keep getting the same list of corrupt files which cannot be repaired, viz fdeploy.dll, fde.dll, gpedit.dll, gptext.dll. It seems I’m not alone in this although seeking help will have to be on a different forum.