If you (or anyone else with problems for that matter) could start off by answering the same set of questions listed in post #106, that would be great.
1) Under Settings / Update & Security / Activation , what does it say?
Windows not activated, error code: 0xC004C003
2) Under Settings / Accounts / Your Account , does it say you are signed in to your verified Microsoft Account?
Yes, it recognizes the email, picture etc...
3) Open an elevated command prompt and type "sfc /scannow". Does that confirm that your system is in a consistent state?
This one was tricky. It found errors, said it was unable to fix them. Then I ran the command in Safe Mode, also didn't work. Tried the DISM command, but it came with a no source error. I resetted my PC from settings, SFC still found problems, so I used my ISO to perform upgrade (not clean install) in order to fix the system files. Now it doesn't show any problems, but the error 0xC004C003 is still there.
4) Is the SKU of both Windows installations (what you in-place upgraded from, and what you later clean-installed) identical? Which SKU is that? (PRO, HOME, etc)
Yes, Pro.
5) Did you upgrade from an insiders preview installation, or directly from W8.x or W7.1?
From Win8.1
6) Are you sure the installation you in-place upgraded from was genuine, activated, and that you logged onto your MS account at least once after upgrading?
Yes, absolutely.
So, now SFC scan shows no errors, but it still doesn't activate. What now? Thanks!