Many of my folders/files became inaccessible, I'm not permitted :(

[drpeppercan]

Take for instance this image file. When trying to open it I get this:

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"It looks like you don't have permission to view this file. Check the permissions and try again."
Then I go to the Properties, Security tab, Advanced, Permissions:

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"You must have Read permissions to view the properties of this object. Click Continue to attempt the operation with administrative permissions."
Then I click Continue:

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"You do not have permission to view this object's security properties, even as an administrative user.
To try taking ownership of the object, which includes permission to view its properties, click Change above."
So I click in "Change", then in the next window, under "Enter the object name to select:", I enter the email address I am using to login to this pc, and hit the "Check Names" button, and the OK button. I try to open that file again, to no avail. It is still telling me that I don't have the permissions to see it.
I know this has to do with recent Windows 10 updates, because these are files I have had for over 10 years now, and I never had a problem backing them up. Until now, all of a sudden they are not my files. Go figure!
Any ideas?
Thanks in advance guys

[drpeppercan]

The MS Installation Key Number is under my name, same as the bill for the computer. I am the only Administrator.
There's 2 other accounts (Unknown), I have no idea about them. Unless they are my wife's and daughter's accounts.
The last one helps Windows Media Player to share its library with network.
By the way, my account at the top, was not here in this list before. I had to manually enter it.

I included a screen-shot of the Properties window of one of the many folders I had to manually add my email address to.