Hi Maria,

This Activation Error Code 0x803F7001 in windows 10 is caused if you installed Windows 10 using flash drive. This Error may also occur if you update your BIOS.
Possibly there can also be issue with Microsoft activation Server and thus you are shown that your windows is not activated.

You can follow the below mentioned methods to solve this issue.

Method 1: Enter the keys.

Go to Start -> Settings- > Update and Security -> Activation -> Change Product Key.
Now enter the Product key of the original OS you had earlier before Upgrading to Windows 10.

For Eg: If you had Genuine copy of windows 8 with Product key, You upgraded your PC to Windows 10 doing Clean install and get Error 0x803F7001.

Then navigate to Change Product key and Enter it there. Following Above steps should activate your Windows, but can not work Every time.

Method 2: Activate Windows using phone
This Method Requires you to use your Phone and Call the toll free number.

• Keep holding Windows key and Press R key to open up Run Command.
• Type Slui 4 in the Run Windows that pops up and hit Enter.
• Next you will require to Select your Country/Region, So do it and Click Next.
• You will be Presented with Toll Free number, Use your Phone now and dial the Number to get the Confirmation ID.
• Once you get the Confirmation ID numbers, Enter them in A to H Field Exactly the way they are Provided.
• Now Click on Activate and its done.

Method 3: Use Windows Media creation tool

In this method you will be required to follow the Cycle of Installing Windows 7/8 or 8.1 whichever OS you have with Product key.
Then after its done, Download Windows Media Creation tool and Use "Upgrade this PC" Feature to Upgrade your PC from your Currently installed OS to Windows 10.

If everything works fine, then you should be able to Upgrade to windows 10 Smoothly.

I hope any of the above listed method will work for you to fix the error 0x803F7001.

Regards,
Lokesh