After trying to install .net 3.5 via the program and features (see below). I was getting unable to install error 800F0906
I am using windows 8.1.
Microsoft has some changes...
Try the full pack Microsoft .NET Framework 3.5 Service pack 1 (Full Package)
I temporarily set User Account Control (UAC) to Never notify.
Start -> Control Panel
Search for uac and select Change User Account Control settings
http://windows.microsoft.com/en-us/windows/turn-user-account-control-on-off#1TC=windows-7
I inserted windows 8.1 dvd and mounted to d drive then executed from powershell.
Enable-WindowsOptionalFeature -Online -FeatureName 'NetFx3' -Source 'd:\sources\sxs'
See http://yellowduckguy.wordpress.com/2012/10/19/windows-8-fix-enable-feature-net-3-5-error-0x800f0906/ for a detailed description.
Enter in cmd (run with administratoir rights):
dism /online /Enable-Feature /FeatureName:NetFX3 /All /Source:E:\Sources\SxS /LimitAccess
(e: is your DVD drive)