Windows 8 and .Net Framework 3.5
When you are unable to install .net 3.5 (includes .NET 2.0 and 3.0) on windows 8 from “Program and Features” Turn Windows Features oN or Off. Error number 0x800F081F.
Perform following from command prompt (Elevated mode)
dism /online /enable-feature /featurename:NetFx3 /all /source:D:\sources\sxs (D: where your Widows installation media or location)