Dealing with activation problems
The first thing to do is to check Settings, Update & Security, Activation to see if your copy of Windows has been activated. If you see Connect to the Internet to activate Windows, either your network connection isn't working or the Windows activation servers are busy. If not you can click Activate, but often it's less frustrating to wait a couple of days; many systems will activate automatically in the background.
If you still can't activate, try using a different network connection – you can't activate Windows if you're connecting through a proxy server that uses basic authentication (where you have to type in a username and password for authentication).
If you see error messages 0XC004E003, 0x8007000D, 0x8007232b or 0x8007007B, they usually mean that the activation servers are overloaded and the installer can't reach them to validate your installation ID.
Automated phone activation
If you don't want to wait (or you suspect the problem is your network connection), you can try an automated phone activation. Press Windows-R or type this command straight into the Cortana search box (and select Run command from the Cortana results):
This opens a box with a dropdown list of countries. Choose yours and you'll see both the free number to call and your Installation ID (divided into groups to make it easier to read) – take a note of it, call the number and type in your Installation ID, then click Next on screen. The Microsoft automated system will read out an installation key that you can type into the SLUI dialog box.
If the SLUI command doesn't run, you may need to start it from an admin command prompt – right-click on the Windows key and choose Command Prompt (Admin).
If you want to reset your product key and force activation, you can use the command line for that too. Open an admin command prompt and type:
Now press Enter and restart your PC, then enter the product key as normal and force activation by opening an admin command prompt and typing:
Again you need to restart.
If you can't type in the product key for any reason, at the admin command prompt, type:
SLMGR.VBS -IPK XXXX-XXXX-XXXX-XXXX
(Fill in your product key instead of the Xs, then restart).
Error 0xC004F061 means that you didn't have a previous version of Windows to upgrade from (if you used to run Linux or you've just reformatted or replaced your drive). Either install Windows 7 or 8, or use your Windows 7 or 8 product key (if you're installing a new enough build of Windows 10 – at least build 10565).
Error 0xC004C008 means that the product key you're trying to use has been used to activate another PC already – if it's a key that can activate multiple systems, then you've reached the limit.
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Mary (Twitter, Google+, website) started her career at Future Publishing, saw the AOL meltdown first hand the first time around when she ran the AOL UK computing channel, and she's been a freelance tech writer for over a decade. She's used every version of Windows and Office released, and every smartphone too, but she's still looking for the perfect tablet. Yes, she really does have USB earrings.