0x803F7001
Windows found no valid license for this device, usually after a big hardware change such as a new motherboard.
How to fix it
- Make sure you are signed in with the Microsoft account linked to the license.
- Go to Settings > System > Activation > Troubleshoot and choose "I changed hardware on this device recently".
- Or enter a product key.
Is it serious?
Fixable if the license was linked to your Microsoft account before the change.