Step #1 Get the MSDM key

  1. Download get_win8key
  2. Naviate to get-win8key folder
  3. Click on File > Open Command Prompt as Administrator
  4. Type get_win8key.exe > key.txt and enter

Step #2 Create Media

Create the media with Windows Installation Media Creation Tool

Language:  English  
Edition: Windows 8.1 or Windows 8.1 Pro  
Architecture: 64-bit (x64)  

Step #3 ei.cfg mod

  1. Naviate to install folder (from step #2)
  2. Click on File > Open Command Prompt as Administrator
  3. notepad \sources\ei.cfg
  4. copy and paste the content below
[EditionID]
[Channel]
OEM  
[VL]
0  

Step 4

Install Windows 8.1 using the newly created media and the MSDM key from step #1