Something I have run into a few times now which is an annoying timewaster is the following error:

Error While Enabling Windows Feature netfx3

You’ll get it on windows 2012 installations when installing SQL 2012(And probably lower versions) and it’s caused by dotnet 3.5not being enabled on the windows installation. It’s frustrating because it happens during the actual installation and is not flagged in any of the pre-requisite checks.  This is because Windows assumes it either has access to the install media to install it from, or can download it from the internet.  On your SQL Servers you shouldn’t have direct internet access, and you are unlikely to have the install media lying around.  At any rate – here’s how to fix it:

1.  Place the install media back to it’s original location(Most likely the CD drive).

2.  From Server Manager choose ‘Add Roles and Features’.

3.  Add ‘.NET framework 3.5 features’.

4.  Now redo your SQL Install and you should be fine.