I buy cheap password-protected laptops at auction and discover the passwords using Ophcrack.
Step 1: Make sure that you've got a blank USB memory stick available.
Step 2: Download Rufus to your own computer. (It's a little program that burns ISO files to USB drives).
https://rufus.ie/
Step 3: Download the Ophcrack Vista Live CD:
http://ophcrack.sourceforge.net/download.php?type=livecd
(You're not actually using a CD. The download is simply an ISO file which you can burn to a USB memory stick).
Step 4: Use Rufus to burn the ISO file to your USB memory stick.
Step 5: Eject the memory stick and insert it into the locked computer.
Step 6: Boot the locked computer up. If it's already configured to look for an operating system on a USB drive ahead of one on its hard drive it will run Ophcrack. If nothing happens you'll need to go into the BIOS of the locked computer to change the boot order and then try again.
Rufus instructions here:
https://www.lifewire.com/how-to-burn-an-iso-file-to-a-usb-drive-2619270
Ophcrack instructions here:
https://www.passmoz.com/how-to-use-ophcrack.html
(NB: It's 'Part 2' which you need there)