Is forums.microsoft.com/technet no longer active? 
Because I cannot post this there, I am posting it here.

Windows 8.1 x64, AMD Phenom X3 2.3GHz, ASUS M4A785M,
Radeon 5450, 4GB Crucial PC2-6400, 111GB Mushkin Chronos SSD

File Sharing for MS Networks is always turned off.  I have temporarily enabled Sharing on the data volume (D:).  DEP is enabled only for essential Windows programs.
Protection is on for the system volume (C:) and off for the data volume (D:).

Avast! free anti-virus and Malwarebytes (free) show no infections or problems.  I am not aware of any previous infestation.

Without warning or explanation, why or what for, volume D: becomes read-only, except for the Recycle Bin.

From the top of the D: volume directory hierarchy to the bottom, the "Read-only" circle is filled, and it stays filled, whatever I do.  I uncheck "Read-only" for volume D: or any folder or file on D:, but without success. When I click "Apply" or "OK", the "Read-only" circle is filled again.
I grant "Full Control" to Users and Authenticated Users, just as SYSTEM and Administrators have.
I can modify files in "My Documents" on the data volume (D:), but not files in other folders.
I disable (and enable again) inheritances to subfolders and files, which remain read-only regardless.

Windows operates normally, even though the system volume (C:) is almost all read-only.
On C:, Bootmgr and all folders, including $RECYCLE.BIN, are read-only. 
"Read-only" is unchecked only for BOOTNXT, Log.txt, pagefile.sys, and swapfile.sys.

Being unable to change or modify files on my data volume (D:) has me at a standstill.

Thank you for any help you have to offer.

• Edited by gospelmidi Wednesday, July 22, 2015 5:37 PM

Now when I uncheck the read-only attribute for each folder on D:, I can modify the files in that folder, even though the read-only attribute for the folder still appears to be on.  I have no idea what I changed that made modifying the files possible.  Volume D: is now completely unlocked for modifying and saving files. 

I didn't touch the Registry.  BTW, in File Explorer, the preview pane is off.

Might it be relevant that there are icons on the desktop for some of the folders on volume D:?

Because the Microsoft firewall is on, and File Sharing for MS Networks is off, I don't THINK there is a prankster intruder trespassing in my PC.  I suppose that is possible, but there's not much on my 111 GB SSD to interest a hacker - no SSN, no credit card numbers, no password list, no love letters...

The randomness of this on-again, off-again read-only locking of my own files and documents is maddening.  I never know when I begin editing a file whether I will be able to save it or not.  It's similar to writing a "dissertation" ;^) on a forum and clicking save, only to find out that the forum has timed out or logged me out.

But I suppose it's not random at all.  I just don't know what I changed.  When I find out, it will no longer seem random, but perfectly orderly.

• Edited by gospelmidi Thursday, July 23, 2015 3:53 AM

Now when I uncheck the read-only attribute for each folder on D:, I can modify the files in that folder, even though the read-only attribute for the folder still appears to be on.  I have no idea what I changed that made modifying the files possible.  Volume D: is now completely unlocked for modifying and saving files. [But see my next post:  80 minutes later, D: is locked up again.]

I didn't touch the Registry.  BTW, in File Explorer, the preview pane is off.

Might it be relevant that there are icons on the desktop for some of the folders on volume D:?

Because the Microsoft firewall is on, and File Sharing for MS Networks is off, I don't THINK there is a prankster intruder trespassing in my PC.  I suppose that is possible, but there's not much on my 111 GB SSD to interest a hacker - no SSN, no credit card numbers, no password list, no love letters...

The randomness of this on-again, off-again read-only locking of my own files and documents is maddening.  I never know when I begin editing a file whether I will be able to save it or not.  It's similar to writing a "dissertation" ;^) on a forum and clicking save, only to find out that the forum has timed out or logged me out.

But I suppose it's not random at all.  I just don't know what I changed.  When I find out, it will no longer seem random, but perfectly orderly.

• Edited by gospelmidi 8 hours 45 minutes ago

Locked out again.  Cannot save files.

Created a new folder; it is read-only for its files from its origin.

Copied files to the new folder.  Cannot save modified files.

I don't dare plug in a USB thumb drive, lest this configuration migrate to it and make it unusable.

I am virtually locked out of my own computer.

It was not like this a few months ago.
If there is a specific Windows Update which caused this, please allow us to remove or disable it.

Why has Microsoft, from Windows 3.0 forward, tightened operations and files until it is almost impossible to use a Windows computer?  Home users don't want an Enterprise system that removes even basic operations, such as modify and save a data file, to protect file security.

What good is a handcuffed operating system that prevents home users from accessing and modifying their own files?  This is no better than running Windows from a read-only DVD with no writable storage.  I can't imagine any scenario where this would be desirable.  So why implement it at all and make it possible for a user to so configure it, even by mistake?

• Edited by gospelmidi 21 hours 54 minutes ago

Locked out again.  Cannot save files.

Created a new folder; it is read-only for its files from its origin.

Copied files to the new folder.  Cannot save modified files.

I don't dare plug in a USB thumb drive, lest this configuration migrate to it and make it unusable.

I am virtually locked out of my own computer.  It was not like this a few months ago.

If there is a specific Windows Update which caused this, please allow us to remove or disable it.

• Edited by gospelmidi 16 hours 14 minutes ago head cooled