The How-To Geek posted an excellent overview of slmgr, a tools used to modify and control Windows Licensing:
Windows activation is designed to be as foolproof as possible, so Microsoft’s graphical tools keep it simple. If you want to do something more advanced like remove a product key, force an online activation, or extend the activation timer, you’ll need Slmgr.vbs.
What do you do, however, if Windows still comes up “Not Genuine” and will no longer rearm? Using a KMS server, this just shouldn’t happen, but in reality it occurs all the time. In the past, we have taken to wiping the machine and starting over, but recently I actually had two recently imaged machines do this!
I found out that in these two cases, I could actually use System Restore to take it back to a previous restore point before things went wrong! Please note that this will not always work, and I really did not expect it to work this time. The only conclusion I can come to is that an update did not properly apply and cause the issue to begin with.
At any rate, it might save someone some time.