Steps taken to fix the “.net 3.5 not installed on Windows 10″ issue:
1. followed this blog at [http://www.kunal-chowdhury.com/2015/08/windows-10-dotnet-framework.html] and [http://www.kunal-chowdhury.com/2015/07/download-windows-10.html]
2. Downloaded the media creation tool *MediaCreationToolx64.exe*
3. Ran the .exe and chose the 2nd option for creating installation file then select the ISO file and saved to c:\Documents\Windows.iso; it took more than 1 hour to download and created the .iso image for Windows 10
4. After the windows.iso was created on C:\..\Documents, right clicked on the .iso file and mounted to E: drive
5. Executed command:  DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:E:\sources\sxs

Microsoft Windows [Version 10.0.10586]
(c) 2016 Microsoft Corporation. All rights reserved.

C:\WINDOWS\system32>DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:E:\sources\sxs

Output indicates this finally succeeded:

Deployment Image Servicing and Management tool
Version: 10.0.10586.0

Image Version: 10.0.10586.0

Enabling feature(s)
[==========================100.0%==========================]
The operation completed successfully.

C:\WINDOWS\system32>
C:\WINDOWS\system32>

6. Went back to the Windows Features On/Off and now the .Net Framework 3.5 checkbox is checked, which meant that the .net 3.5 is now installed on my Windows 10 machine.