Microsoft Diagnostics and Recovery Toolset (DaRT) is one of the most popular tools that lets you diagnose or repair your computer without booting into Windows. After booting into DaRT, you can easily reset forgotten local admin password on Windows 10 / 8 / 7 installation using the built-in recovery tool - Locksmith.
Reset Forgotten Windows Admin Password with DaRT's Locksmith
Boot the target machine using the DaRT Recovery CD. Select your keyboard layout and navigate to Troubleshoot -> Microsoft Diagnostics and Recovery Toolset.
The next screen will list the operating systems detected on your computer. Simply choose the Windows system you can't log in to with admin account.
Now, you can access a set of tools in DaRT. To reset a forgotten Windows password, you have to select the Locksmith recovery tool.
This will launch Locksmith wizard. Click on Next.
Select the admin user from the Account drop-down list. Create a new password and click on Next.
If you have a local policy on the system that enforces password length or complexity, the new password must comply with this policy.
Click on Finish. Your account password will be changed when you restart Windows.
DaRT Locksmith is one of the most powerful tools to reset forgotten Windows admin password. But sadly, it is also the most ignored or least used tool by the Windows users as it's freely available to Microsoft Software Assurance customers only. If you have no access to DaRT Locksmith, try the best alternative - WindowsUnlocker.