Installing Windows 8 with different product key

New laptops often are shipped with the Windows product key stored in the EFI/BIOS/whatever. The result is that you don’t get a product key prompt any more. Great for reinstalls, as copying the key by hand is very error-prone. However, when I wanted to install a fresh Win8 Pro version, the embedded “Home” version key wasn’t accepted and the installer did not ask for another key. It was simply impossible to install Windows 8 Pro.

This blog post will describe how I got it installed in the end.

1. Get a USB stick that’s large enough - 4 GB or more should do it.

2. Transfer an ISO file of the Windows installation disk to the USB stick, using Microsoft’s USB DVD tool. Please note that this will erase any contents of your USB stick.

3. On the USB stick, create a file sources\PID.txt that contains:

   [PID]
   Value=XXXXX-XXXXX-XXXXX-XXXXX-XXXXX
   

   Replace the XXXXses with your product key.

4. Copy all files from the USB stick back to your harddisk.

5. Reformat the stick as FAT32. Microsoft’s tool has formatted it as NTFS, which is not supported as a boot device for newer laptops (i.e. the ones you need this trick for in the first place).

6. Copy all files back from your harddisk to the USB stick.

7. Eject the USB stick. You need to do this cleanly (don’t just jank it out) to ensure that all files were written to it. You don’t want to have to redo your installation because it failed halfway, do you?

8. Boot from the USB stick to install Windows. It will not prompt for the product key, but use the one you specified in sources\PID.txt.