How to Create a New Admin Account in Windows 10 When You Can’t Login With Existing Account

(taken from HowtoGeek.com)

First, start by booting your Windows 10 installation into the setup by changing the boot order in your BIOS to take priority with the CD, or use the ISO as a startup disk instead.

Once the setup begins, hit Shift+F10.

This will bring up a command prompt. From here, we’re going to use the command prompt to replace the Utility Manager (“Ease of Access”) at the login screen with cmd.exe with the following commands:

move d:\windows\system32\utilman.exe d:\windows\system32\utilman.exe.bak

copy d:\windows\system32\cmd.exe d:\windows\system32\utilman.exe

Once this is complete, use the command “wpeutil reboot” to restart the machine.

After you’re back at the login screen, click the Utility Manage (Ease of Access). If everything went right, you should see a cmd.exe launch like the image below.

This is the prompt you’ll use to create a new administrative user from the login screen. Type in the following commands, replacing <username> with the name you’d like to assign to the new account (no carrots).

net user <username> /add

net localgroup administrators <username> /add

Now close the prompt, reboot, and you should see your new user in the login screen.

With this new account you can change the password for the old account as long as it is a local account. If the old account is linked to a Microsoft account you’ll have to contact Microsoft online or on the phone. (Another good reason NOT to have a MS account!)