How to Unlock Surface Pro 4 If You Forgot Windows 10 Password?
Use a working PC (because you're locked out of Surface Pro tablet) to download PCUnlocker Enterprise. After you've downloaded it, unzip it to a local folder. You'll see a CD image: pcunlocker.iso.
Next choose "Burn to USB Flash Drive" and select your USB drive from the list. Select "GPT (required for UEFI boot)" under Partition Style. Click Start Burn.
After the USB drive is burning successfully, insert the USB drive into the USB port on your Surface Pro 4. Make sure Surface Pro is turned off. Hold down the volume-down (-) button and press the Power button, release two buttons until you see the Surface logo on the screen.
You'll be presented with the PCUnlocker screen. Select one of your user accounts and click on "Reset Password" button. It will remove your Windows 10 password immediately.
Reboot your Surface Pro and unplug the USB drive. You can then sign into Windows 10 without typing a password. This procedure also works with Surface Pro, Surface Pro 2 and Surface Pro 3.