Thanks again for taking your time to help. I'm very grateful.
Your recommendations are fairly 'root and branch' but I guess that's the way to go now. I regularly backup with Acronis so that is all in place. It will take some time but I'll let you know the outcome when I'm done.
There are so many variables and imponderables that not all software will work on all systems.
LR is now at V1.3.1
Has KAV quarantined any important file or blocked an important files use.
Instead of just turning KAV off, disable its service. You may have to do this in Safe Mode as this is a security feature against malware attacks turning it off in normal mode.
All systems slowly break in time so I wouldn’t be surprised if it worked from a clean install.
Take an image of your system using Acronis True Image or Ghost.
Now install Windows clean and then install LR and see if it works. If it does then it is a system problem.
Now restore your image (verify it on its creation and verify it on it restoration) and then you will know that it is problem with your current setup.
Also backup any critical data as images do corrupt even if they are verified as sound.