That is because you got the OEM copy ... Intended to be boxed with a pre-built system, by an Original Equipment Manufacturer . . .
. . . In this case, it is *YOU* who is the OEM (congratulations!) . . .
. . . Just remove the disk from the packaging (without messing up any labels or stickers) and proceed with the install . . . It will ask you for that key # and I would not have it attached to the internet until your full software build/install (apps, etc) is complete ... Just saying that you do not want to validate until you are sure you aren't going to crash ... By "validate" ... I am talking about online registration ... you will still need to enter your software key code (16 digit alpha-numeric?) during the DVD install. Fine to do...