How can I activate windows 10 free without product key?

How to activate Windows 10 free? Here are some options you can consider:

1. Digital License (Digital Entitlement):
If your previous Windows 10 installation was activated with a digital license linked to your hardware, Windows should automatically activate once connected to the internet.  

Check Activation Status:

• Go to Settings > Update & Security > Activation to see if Windows is already activated.

Troubleshooting Activation:

• If it's not activated, you can try running the Activation Troubleshooter:
• In the Activation settings, click Troubleshoot and follow the prompts.
• Sometimes, Windows can reactivate automatically if it detects previous activation tied to your hardware.

2. Reusing the Same Hardware:

• Since you've upgraded hardware, especially the motherboard, Windows might see this as a new device, which can break the activation link.  
• If you've previously linked your Windows to your Microsoft account, the activation might be restored by signing in with that account.

3. Upgrade from Genuine Windows 7/8:

• Although the free upgrade offer officially ended in 2016, Microsoft still allows activat Windows 10 free with a valid Windows 7/8 key.  
• If you have a valid Windows 7 or 8 key, you can enter it during installation or via Settings > Update & Security > Activation.