Here you will find some common topics on why you might be having trouble activating Windows.
Missing product key or digital license
Windows 10 activation requires either a 25-character Windows product key or a Windows digital license.
- A digital license (called a digital entitlement in Windows 10, Version 1511) is a method of activation in Windows 10 that doesn't require you to enter a product key.
- A product key is a 25-character code used to activate Windows. What you'll see is PRODUCT KEY: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX.
A different version of windows or product key was used during repair
If Windows was activated before your PC was repaired or rebuilt, reinstall your original version of Windows and re-enter the product key included with your PC or original copy of Windows.
One copy of Windows was installed on multiple PCs
If you have one copy of Windows and try to install it on more than one PC, activation will not work. Microsoft Software License Terms only allows one copy of Windows to be activated on one PC.
For each PC you will need to purchase a copy of Windows for each one.
Counterfeit software
A counterfeit is a copy that wasn't published and licensed by Microsoft. Activation only works with genuine copies of Windows. If you do find out you have a counterfeit copy, you must buy a new copy of Windows.
Pre-owned PC
If you bought a PC with Windows already installed, it's possible that the seller used the product key on more PCs than allowed by the Microsoft Software License Terms.
Ask the seller for the original Windows DVD and product key. If the DVD and product key aren't available, or if you tried them and still can't activate your PC, you must buy a new product key or another copy of Windows.
Hardware changes
If you made significant hardware changes to your PC, such as replacing your hard drive (HDD or SSD) or motherboard, Windows may no longer be activated.
For Windows 10 (version 1607 or later), you can add your Microsoft account to help you reactivate Windows 10 after making a hardware change.