No. Sadly, replacing the old drive made no difference. Removing the old drive and putting in a brand new drive made no difference, either.
I trawled through a lot of Toshiba forum Q & As, and tucked away somewhere I found a list of Toshiba laptops that are guaranteed to work with Windows 10. This particular laptop was not amongst them ... I have just gone back to the Toshiba site to try to find the list, but the site won't recognise my laptop serial number or series code as valid, so, since I bought it in 2012, I am guessing it is simply out of date, out of support, a hasbeen.
I do thank you for your time looking at this issue - I know it is down to the Windows 10 update knocking out the registry entry/entries for the CD/DVD drive because hardware-wise the drive itself is clean and in working order.
Can we close this thread down as "Not Resolvable", do you think?