>get ISO here http://forums.mydigitallife.info/threads/47732-The-Windows-8-1-%28-amp-related%29-Repository#a7i
>copy to USB stick using http://www.microsoftstore.com/store/msusa/html/pbPage.Help_Win7_usbdvd_dwnTool (don't let the name fool you, it works with Win 8.1 too)
>install with serial from http://technet.microsoft.com/en-us/library/jj612867.aspx
>get Microsoft Toolkit here http://forums.mydigitallife.info/threads/28669-Microsoft-Toolkit-Official-KMS-Solution-for-Microsoft-Products
>run it and press the Windows button, then Activate