Installing SQL Server 2012 on Windows 8 is a pain, because SQL Server 2012 needs .NET 3.5. The problem is activating .NET 3.5 in Windows 8 via Turn On/Off Windows features won’t help because .NET 3.5 is considered as an on demand installation feature. Windows Update also fail to address the need. There are good articles describing the exact problem in detail.
You can install the .NET 3.5 in Windows 8 using your installation media and activating the feature. Simple. Insert your installation media or mount the Windows 8 image in a drive.
Open CMD as administrator
Type the following
DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:J:\sources\sxs
Here J:\ is the drive of my installation media.
You will see a similar screen like this, wait for the installation completes.
Done ! Now .NET 3.5 has been installed successfully on your Windows 8 PC.
Get the MS Word document which explains the .NET 3.5 installation scenario on Windows 8 and Windows Server 2012 in detail from the link below