Think I've got to the bottom of this now,
I've uninstalled completely and reinstalled, after trying uninstalling & reinstalling LW on its own.
After each reinstall, I've had parts of the program working that were not working previously, but other parts that were not working, now working. For example, after reinstalling I could not access the LW edit materials window from within the materials palette, which I could do previously, but I can now render objects with LW, which I couldn't do before.
I put the issues I've had down to the anti-virus & security software I'm running, (Norton),
I'm fairly sure if I was to disable it and reinstall TurboCad & LW's, it would be fine. But I'm loathe to do this, in view of the current cyber climate, with all those nasties flying around out there.