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!