Install .NET 3.5 on Server 2012 or Windows 8, 10, 2012

Make sure you have the Windows 8, 10 or Server 2012 installation disc in your drive

In the example below, the installation disc is in the D:\ drive

Open an administrative PowerShell command window and enter the following:

Server 2012
Install-WindowsFeature –name NET-Framework-Core –source D:\sources\sxs

Windows 8, 10
Enable-WindowsOptionalFeature –online –featurename NetFx3 -source D:\sources\sxs

Wait until installation is complete, then run Windows Update to get the latest patches and fixes