Restore Previous Versions always says "There are no previous versions"

Bingo! I found what I was looking for on a couple of other sevenforum threads, and am summarizing what I did here to make the previous versions available in case it helps anyone else.

How to Fix ‘Previous Versions Not Available’ (Windows 7, SP1)

Presuming that you have a regular schedule of creating Windows Backup and/or automatic System Restore Points. Backup you have to set up yourself. System restore points are created automatically by Windows at start up by default.

1. Check that System Protection for the C drive and other drives you wish to be included in the backup is ON: Control Panel > All Control Panel Items > System > System Protection > Select drive > Configure > Restore system settings and previous versions of files or Only restore previous versions of files.

2. Check that files that are not system files are included in Windows Backups: Control Panel > All Control Panel Items > Backup & Restore > Change settings > Select your backup drive and click Next > Check your backup selection

3. Check status of various Services: Start key > Type 'Services' and press Enter

Volume Shadow Copy – Manual (may be Started or Stopped)
Server – Started and Automatic.
TCP/IP NetBios Helper – Started and Automatic.
Workstation – Started and Automatic.

4. Check that file and printer sharing is on: Control Panel > Network and Internet > Network and Sharing Center > Change Advanced sharing settings.

5. Check that the relevant drives used by Windows Backup for both the files to back up and for saving the backup are shared: Computer Management > Disk Management > Right-click the drive > Properties > Sharing > Advanced Sharing > Tick ‘Share this folder’

You can also check which drives are shared by looking in: Computer Management > System Tools > Shared Folders > Shares. Shared drives will have a $ behind the drive letter. E.g. C$ and G$

6. Open Regedit (Start key > Run > type Regedit > press Enter) and backup your registry (File > Export)

Locate and then click the following registry sub-key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanmanServer\Parameters

If the AutoShareServer and AutoShareWks DWORD values in the LanmanServer\Parameters
sub-key are configured with a value data of 0, change that value to 1 (right-click > modify > 1). When done it should look like this:

AutoShareserver REG_DWORD 0x00000001 (1)
AutoShareWks REG_DWORD 0x00000001 (1)

I noticed that someone had noted that AutoShareWks was absent on their computer, but it made no difference to the results.

7. If previous versions from both Restore points and Backup are not showing, and you want to see the previous versions in the Backup location, then try running the registry modifier (and reboot) available at:

Previous Versions - Hide or Show from Backup Location

I tried the Option 2 mentioned on this page (run the Local Group Policy Editor, gpedit.msc, and in the left-hand pane: User Configuration > Administrative Templates > Windows Components > Windows Explorer > Previous Versions > Hide previous versions of files on backup location > Not Configured or Disabled), but it did not reveal the previous versions in the Backup. The registry modifer however did the trick. Enabling the ‘Hide’ option hides previous versions in the Backup location.

8. Reboot, and check that previous versions are now available (select and right-click a file in Windows Explorer > Restore Previous Versions). You may have to open, edit and save a document before previous versions will show up. If autosaving of restore points is turned off, you will probably have to invoke a Windows Backup before you will see previous versions listed.) Also, on my computer, if I check Restore Previous Versions of a document from within MS-Word, only restore point versions are listed. Doing the same from Windows Explorer, both backup and restore point versions are present.... ("And that's all I have to say about that!" - Forrest Gump).

PS. It is perhaps worth mentioning that a friend whose computer had been attacked by the Cryptowall ransomware virus had ALL his user files on ALL his attached drives encrypted. After several days of trying everything he could think of to restore access to the files, he tried Shadow Explorer, which revealed that his shadow copies were all intact and unencrypted.