Many users who recently got the big November Update or Threshold 2 (TH2) update have been going through the activation issue again. Several users are reporting that their Windows 10 install was deactivated after installing the update.
Method 1 of 4
Use your Windows 7/8/8.1 product key to activate Windows 10
Users can now activate Windows 10 using a genuine product key previously being used for Windows 7 or Windows 8.1.
Now if you have lost the product key of your previous Windows version, you can’t recover it unless the product key embedded in the firmware or you still have the backup of your previous Windows version. If you purchased a PC pre-installed with Windows 8 or above version, the product key is likely embedded in the BIOS/UEFI firmware. In that case, you can try out third-party tools to recover product key from BIOS/UEFI, and then manually enter the same key in Windows 10 to get it activated.
To enter the product key and activate Windows 10:
Step 1: Open Settings app.
Step 2: Click Update & security.
Step 3: Click Activation.
Step 4: Click Change product key, and then enter your 25-character Windows 7/8.1 product key and then click Next button. Make sure that your PC is connected to the internet while clicking the Next button.
Method 2 of 4
Contact Microsoft support
Contacting Microsoft support is easier than ever now thanks to the Contact support app in Windows 10.
If you’re certain that your Windows 10 install was activated before the update, or if you are unable to activate Windows 10 with November or Threshold 2 update using your genuine Windows 7/8.1 serial key, you can have a chat with Microsoft support team via the Support app to sort out the issue.
Method 3 of 4
Go back to the previous build
If Windows was deactivated after installing an update, try restoring to a previous date through previously created restore point. And if your Windows 10 was deactivated after a big update like Threshold 2 update, you can roll back to the previous build by opening Settings, clicking Update & security, clicking Recovery and then clicking Go back to an earlier build.
Method 4 of 4
Perform a clean install of Windows 10
At times, product key recovery tools might fail to recover the original product key embedded in the BIOS/UEFI and might display a generic key instead. If you’re sure that there is a product key in your PC’s BIOS or UEFI firmware, then go ahead and perform a clean install of Windows 10.
The Windows 10 setup automatically picks up the key stored in the BIOS or UEFI firmware and activates your copy of Windows 10. And before doing so, backup all data from your PC, especially from the drive where you plan to install Windows 10.
Use the Media Creation Tool to download Windows 10 ISO from Microsoft, prepare a bootable USB out of the ISO, and then install Windows 10 from the USB drive.