A Microsoft sugere o seguinte (você mencionou você quer evitar a reinstalação, mas eu, pessoalmente, faria isso apenas dessa maneira, dando meu PC longe):
If you want to recycle your PC, give it away, or start over with it, you can reset it completely. To reset your PC
1. Swipe in from the right edge of the screen, tap Settings, and then tap Change PC settings. 2. Tap or click Update and recovery, and then tap or click Recovery. 3. Under Remove everything and reinstall Windows, tap or click Get started. 4. Follow the instructions on the screen.