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Create a Pre-Activated Windows 8.1 Update Pro with Media Center iso!  (This ONLY works if Windows 8.1 Update with Media Center is allready activated)
You will have to make a seperate iso for each computer.  (You will also need to know the Media Center Key used for each PC so you can inject it into the iso)
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Download The Windows Assessment and Deployment Kit Here - http://www.microsoft.com/en-us/download/details.aspx?id=39982
Run it and uncheck all boxes apart from deployment tools, install deployment tools

Create a folder on your C: drive and name it win81
Then create 3 subfolders inside the win81 folder and name them as follows: iso, wim, mount
Next extract your windows 8.1 iso to the iso folder C:\win81\iso
Then move the install.wim from C:\win81\iso\sources to the wim folder C:\win81\wim

Now open Deployment and imaging tools CMD as administrator and enter these 3 commands, one at a time



Dism /mount-wim /wimfile:C:\win81\wim\install.wim /index:1 /mountdir:C:\win81\mount

Dism /Image:C:\win81\mount /Get-TargetEditions

Dism /Image:C:\win81\mount /Set-Edition:ProfessionalWMC



(Make sure you can view hidden files and folders if you can't see the data.dat or tokens.dat in the steps below)
Delete C:\win81\mount\Windows\System32\spp\store\2.0\data.dat and replace it with C:\Windows\System32\spp\store\2.0\data.dat
Delete C:\win81\mount\Windows\System32\spp\store\2.0\tokens.dat and replace it with C:\Windows\System32\spp\store\2.0\tokens.dat

Before you enter the next 4 commands, replace xxxxx-xxxxx-xxxxx-xxxxx-xxxxx with your WMC key



Dism /Image:C:\win81\mount /Set-ProductKey:xxxxx-xxxxx-xxxxx-xxxxx-xxxxx

Dism /unmount-wim /mountdir:C:\win81\mount /commit

imagex /flags "ProfessionalWMC" /info C:\win81\wim\install.wim 1 "Windows 8.1 Pro with Media Center" "Windows 8.1 Pro with Media Center"

Dism /Export-Image /SourceImageFile:c:\win81\wim\install.wim /SourceIndex:1 /DestinationImageFile:c:\win81\iso\sources\install.wim /compress:maximum



Now you will need to create an ei.cfg file, Copy and paste the following into notepad and save as ei.cfg



[EditionID]
ProfessionalWMC

[Channel]
Retail

[VL]
0



Place the ei.cfg file you just made into C:\win81\iso\sources
Enter the final command to build the iso



oscdimg -bC:\win81\iso\boot\etfsboot.com -h -u2 -m -lWIN81-PRO-WMC C:\win81\iso C:\win81\ProWMC.iso



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You now have a Clean Pre-Activated Bootable Recovery iso for your computer... Format your dirty pc with it and watch it reactivate when online :)
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