Windows 10 Update. Now Live Mail accounts, inbox Storage Folders ALL GONE

I am using WLM under Windows 10 and until today it has been working fine.  Windows 10 installed an update when I turned off my computer last night.

When I started my computer this morning and opened WLM all my data (except contacts) has been deleted. No Accounts, no Inbox, no Storage Folders. It shows Drafts, Sent and Deleted, but they are all empty.

I went to the location where the data is stored (C:Windows.old/users/myusername/AppData/Local/Microsoft/Window Live Mail) and the folders all have creation dates of today and times of 09.14 (when I opened WLM) or later. None of the Storage Folders are there.

I tried System Restore, but the only two restore points on offer were around 11am today. I chose the earliest one, but it did not help.

I have looked in the recycle bin and cannot see any of the folders there.

I have tried right clicking on the folder and selecting 'Restore Previous Versions' but only one version is on offer and that is timed around 11am today so that will be useless.

I looked at the backup which I have running each evening under Control Panel 'System and Security' which I thought would contain all my data only to discover that the mail files are not part of that backup. 

I do not keep my mail on my ISP's web server, it is all local so I cannot re-download it.

I need to know how to recover this very important data. I would also like to know how it is possible for it to be arbitrarily deleted in the first place?