Windows 8.1: How to install .NET 3.5
Overview: When you try to install .NET 3.5 through the control panel you have the choice to search Windows update servers or specify media. In either case you are unable to install .NET with an error.
1. Copy the d:\SXS folder from the media to the C drive.
2. Open and Administrator command prompt.
dism.exe /online /enable-feature /featurename:NetFX3 /Source:c:\sxs /
4. .NET has been successfully installed.