■ Greetings, I had this issue on a computer I had. After getting the Win10 upgrade eligible in Windows 8, I became impatient waiting and decided to force load Win 10 myself. I downloaded windows 64 bit and let it install. Had the Key Activation Error 0xC004C003. I followed the advice above of going
here once I had my product key extracted.
The technician logged into my computer remotely and did a diagnostic. He opened a command window and ran:
slmgr.vbs /dlv
^^ this shows how you are currently licensed.
He then ran:
findstr /i /c:"Source OS" c:\windows\panther\setupact.log
^^this provided him with a number which he as able to look up to see internally at MS what my source OS was.
He then ran:
wmic path SoftwareLicensingService get OA3xOriginalProductKey
^^this showed the very same product key I had extracted from my BIOS using the instructions found
here
He then asked me to wait a few moments and he took about 3 or 4 minutes researching on his end.
He came back and told me that I had (errantly) loaded Win 10
Home on a machine that was registered for Windows 8
PRO. He Opened a notepad screen and pasted some questions for me and "waived the mouse over top of it" to indicate he wanted me to enter the following:
My Name:
My Phone:
My Address:
Machine Manufacturer:
Original Key: (I had this ready to paste in)
Once I entered this he generated a Win10 Pro key for me, and applied it for me as well. He then opened a notepad window asking me to save it on my hard drive. but as that happened Windows 10 began the "upgrade" process to Pro immediately, and I lost complete control of the machine to to Win Upgrades.
I was worried as it forced a reboot, that I wouldn't know my new key for certain. But once it completely rebooted automatically twice, I was once again back in the remote control session with the MS tech (automatically, no effort on my part). He again brought up the notepad and pasted in my new Win 10 key and he asking me to save the key in a safe place. I saved it on my network.
All this took about 30 minutes total. Thanks to all above, especially Trkkr19.
Also, I took a sharpie, and I physically wrote both the Win 8 PRO and Win 10 PRO keys clearly with permanent ink on the inside of the case of my computer.