Following on from the above, I went into regedit and looked for any relevant registry keys. I found one, deleted it but that made no difference.
I then did what I had never done before, downloaded and installed a registry cleaner.
I ran that, having told it to look for entries appertaining to viaagp1, viaagp, via technology, prosavage ddr and it found dozens of entries tucked away in the nether regions of the registry.
I shut my eyes, held my breath and told it to delete the lot ( making a backup before doing so.)
This am, the machine started just fine, and the error report in the event viewer did not occur..........woohoo
Not only that, yesterday I spent a lot of time using Photoshop which has been a recipe for a non-shutdown situation and.....................the machine shut down normally and correctly. :clap2:
It is possible then that the opening and closing errors were linked and, I say this quietly in case the machine hears me, that getting rid of all these old registry keys has sorted two problems in one. Time will tell.
Fingers crossed.