( HOW TO INSTALL .NET FRAMEWORK 3.5 on WINDOWS 8 )
In Windows 8 or Windows Server 2012, open a Command Prompt window with administrative credentials (that is, choose Run as administrator).
f installing the .NET Framework 3.5 on demand or enabling it in Control Panel fails, you may get one of the following error messages:
0x800f0906: "Windows couldn't connect to the Internet to download necessary files. Make sure that you're connected to the Internet, and click Retry to try again."
0x800F081F: "The changes could not be completed. Please reboot your computer and try again."
To install the .NET Framework 3.5. Install from the installation media. Located in the D:\sources\sxs directory. Run the following via at a command (run as administrator). Please note to change the drive letter or path to the respected media location:
DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:d:\sources\sxs
SOURCE: http://msdn.microsoft.com/en-us/library/hh506443.aspx