I recently installed Windows 8.  I used my company’s MAK Key which is a volume license key.  Everything installed just fine but I did notice it never asked me for my product key. On a domain, Windows 8 Enterprise automatically determines which servers to activate against using DNS.  This helps with managing your volume license easily.  Now, if you decide to do a 1 off install it will never activate correctly because it is missing the product key.  This is easily resolved. 

• Hit the Windows+R hotkeys to open the Run box and run: slui.exe 3

This will bring up the following window:

Enter your product key and then click Activate.  You should be good to go!