Many end clients will use Windows 8.1 or Windows 10 as agent hardware. Most usual ISO-based password retrieval tools such as NTPassword or KonBoot will fail (mostly with 64bit versions of the OS). A simple and secure way of resetting a local administrator password:
Boot the computer in Windows install using removable media (Windows install disk). You might have to turn off secure boot and/or enable legacy or setup mode in BIOS, depending on your hardware and BIOS .
Press Shift + F10 to load the command prompt
In the command prompt, type the following command:
move c:\windows\system32\utilman.exe c:\windows\system32\utilman.exe.bak
…afterwards:
copy C:\windows\system32\cmd.exe c:\windows\system32\utilman.exe
…and then finally:
wpeutil reboot
System will reboot and load Windows normally. Click on the Utility Manager icon (lower left corner), and command prompt will open. Type in the following commands:
net user TempAdmin /add
net localgroup administrators TempAdmin /add
Log on with your new user called TempAdmin and change the password for any other local account.