Windows 8 and 8.1 do not allow you to install Dot Net 3.5 using an internet connection… which is its default. The solution is to extract the SXS folder from your install media and then run a command line install with the following:
- Insert your Windows 8 (or 8.1) DVD or ISO (in item 3 below, I assume your DVD or mounted ISO is “D”)
- Start an elevated CMD prompt
- Dism /online /enable-feature /featurename:NetFx3 /All /Source:D:\sources\sxs /LimitAccess
Fear not, .NET 3.5 and .NET 4.5 (which is built into Windows 8.1) function nicely together.