I was thinking about the possibility of doing a clean install one day but realized that I don't have a Windows 8.1 Pro DVD with media center. I posted in the Windows forum that I really needed this and one of the Microsoft MVPs stepped forward and came up with a procedure. I am going to share this procedure with everyone BUT you must have a valid copy and license for Windows 8 and a valid key for Windows media center:
 
Download and install The Windows Assessment and Deployment Kit (ADK) for Windows 8.1 (Don't download the Windows 8 ADK as that will not work)
When installing uncheck all boxes apart from deployment tools, install deployment tools only
Create folder on your c drive and name it win82
 
Then create 3 subfolders inside the win82 folder and name them as follows: iso, wim, mount.
 
Next extract your windows 8 iso to the iso folder C:\win82\iso Then move the install.wim from C:\win82\iso\sources to the wim folder C:\win8\wim  (I couldn't find install.wim so I copied this from the Windows 8 DVD)
 
Then open Deployment and imaging tools CMD as administrator and enter the following command 1 at a time
Code: (Don't type the word code)
Dism /mount-wim /wimfile:C:\win82\wim\install.wim /index:1 /mountdir:C:\win82\mount
 
(This took a little while to finish so make sure you wait)
 
Code:
Dism /Image:C:\win82\mount /Get-TargetEditions
 
Code:
Dism /Image:C:\win82\mount /Set-Edition:ProfessionalWMC
 
Before committing changes to the image you can enter your free windows media center key via dism command this will install your key and activate only on the machine you intend to use
Code:
Dism /Image:C:\win82\mount /Set-ProductKey:xxxxx-xxxxx-xxxxx-xxxxx-xxxxx
Code:
Dism /unmount-wim /mountdir:C:\win82\mount /commit
 
Code:
imagex /flags "ProfessionalWMC" /info C:\win82\wim\install.wim 1 "Windows 8 Pro with Media Center" "Windows 8 Pro with Media Center"
Code:
Dism /Export-Image /SourceImageFile:c:\win82\wim\install.wim /SourceIndex:1 /DestinationImageFile:c:\win82\iso\sources\install.wim /compress:maximum
 
Next you will need to create an Ei.CFG file, Copy and paste the following into notepad and save as Ei.CFG
Code: (Don't type the word "code")
[EditionID]
ProfessionalWMC

[Channel]
Retail

[VL]
0
 
place file Ei.CFG in sources folder C:\win82\iso\sources
 
(Ei.CFG Will allow you to install any of the editions without having to enter a product key first)
 
Next to create bootable iso, open the Deployment and imaging tools command prompt as administrator and enter the following command
Code:
oscdimg -bC:\win82\iso\boot\etfsboot.com -h -u2 -m -lWIN8.1-PRO-WMC C:\win82\iso C:\win82\ProWMC.iso
 
I believe this worked for me or at least it seems to have worked but I haven't fully tested it yet. Hope this is helpful to many forum members and kudos to Microsoft MVP Tiger120111 over at the Microsoft forums

That is a good article if you have a retail key. But, if you have a upgrade key for 8. Which I would say the majority do. Since MS was running that special for $15-$39 when it first came out. That method does not work. You will need to download the leaked/MSDN iso. Use a generic key for the version you are installing. Then you use your Windows 8 key to activate.

I wanted to make the 1st post as a way for anyone to install windows 8.1 with WMC without having to install win 7, upgrade, etc. So if you download Belarc Advisor free edition and run it then you should see the windows key for Windows 8.1 with WMC if that is what you are using. Print that key out so you'll have it. You can use this method above in the 1st post to make a fresh install.

What step did you get stuck on? Can you post a screenshot? Oh one thing, you have to make sure the folder win82 that you create has full rights to the administrator. If the rights for the folder indicate trusted installer then you have to change it.