Now 2nd machine wants User/pass to file share on LAN (after update)

We've a couple of machines on a home LAN and this first happened to one of them about a week ago. I asked about it here but no solution. Now it has happened to a 2nd machine and broken the whole LAN.
We've never had a User/password and don't want one.

How can I remove the User/password dialogs and restore the access there was previously?

I did try a system restore but was told "No restore points have been created" and I couldn't get the advice (about System protection) to create one to work.

And advice really appreciated as no LAN access mucks up everything at this end.

I should add the 'update' was the one that added an item to the tray called "Store".

Bumped?
I couldn't quite follow / interpret your answer but I now a solution. It may be overly simplistic, but it worked for me (on both machines) so I offer it here just in case someone else is in the same predicament.

Cause. Unplanned/known windows update. After which a "Store" icon appears in the tray (and who-knows-what else it does)
Problem: LAN now demands non-existent User/Pass.

Solution
Windows Icon - Shift + click Power button
I found a mix of options that varied (and were different on each computer too.)
One that worked here was "Update And Restart" . Ultimately you want a Troublshoot button.
It's the middle one of three. (Quite possibly you can get to it other ways)
From there - Advanced settings - then "Go Back to Previous Build".