Aha, thanks very much for that info.
I thought my user was an admin but I may have set it as a restricted user.
I will remove Avast and monitor.

Thanks again.
I will remove my uploaded log file...

This began happening on occasion a few months ago. Initially it was when watching videos on FB. Now seems to be occurring more frequently and under more circumstances (casual browsing, music...

An update for those interested.
I ended up using tips from both dalchina and das10. The link dalchina provided got me access to the found.000 contents and das10's pointer to retrieving chk files...

Thanks all for your comments, it will take me some time to follow up.
In response to some points:

I don't recall how I mapped My Documents to drive "D" but I remember following a Microsoft...

Running Windows 10 on a Gigabyte motherboard based tower PC.
Have the OS on an SSD and I had mapped "My Documents" to an HDD, assigned drive letter D with volume name "Stores".
The install is about...