Seeing “Windows is not activated” after reinstalling Windows is a common issue and usually does not mean your license is lost. In most cases, Windows simply hasn’t revalidated your device with Microsoft’s activation servers yet.
The following steps resolve the issue in the majority of cases.
First, make sure the PC is connected to the internet. Windows activation requires an active connection and will not complete properly while offline.
Next, run the built-in Activation Troubleshooter. Open Settings, go to System, then Activation, and select Troubleshoot. This tool checks your device’s hardware signature and attempts to re-associate it with an existing digital license.
If activation still fails, sign in with your Microsoft account. If your license is linked to an account, signing in often triggers automatic reactivation without needing to enter a product key.
If you have a 25-character product key, you can also enter it manually. Go to Settings, then System, then Activation, choose Change product key, and enter the key while connected to the internet.
When activation does not succeed after these steps, the cause is usually one of the following: significant hardware changes, a license already in use on another device, or a key that is not valid for standard retail activation.
I wrote a more detailed breakdown explaining why activation fails after reinstalling Windows and how to identify the exact cause in this full guide.
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