Dear Friends As per the thread title Background: I made a minor change in BIOS, to add an asset tag. All good. Upon reboot, Windows thinks I've had a hardware change! I have been through the activation troubleshooter, to no avail. 0xC004C003 I have a valid digital licence, linked to my Microsoft account, as I upgraded from Windows 7 Ultimate x64. I've tracked the issue down to the sync service: it looks to me like Windows can't "talk" to my Microsoft account to see the digital licence. The microsoftaccounts.diagcab troubleshooter identifies the issue, but can't fix it. If anyone knows what to do, I'd be very grateful! Thanks.