I was handed a laptop with Windows 7 Pro and a single user on the laptop with an unknown password. I had a 1 GB flash drive. Ideally, I would have had a 8 GB or larger USB drive that I could put a Windows 7 installer on, but I didn't (would have saved me from needing Linux).
These steps require medium level tech savvy. If you've never worked in a DOS prompt before or don't know what that means, you won't have much luck with these steps.
Here's what I did step by step:
On another laptop, I did these things:
Downloaded Linux Live USB Creator from here: http://www.linuxliveusb.com\
Downloaded System Rescue CD from here: http://www.system-rescue-cd.org/Download
Made a bootable System Rescue CD on the 1 GB USB flash drive
On the laptop with the unknown password, I ran these steps:
Booted to the Linux distro we put on the USB drive
Started the default Linux version when presented
ran "startx" to start the GUI
opened up a terminal/CLI prompt
ran mount -t ntfs-3g /dev/sda1 /mnt/windows
** note that /sda1 might not be the location of your C drive where Windows is located, might be sda2 or sda3
ran cd /mnt
ran cd windows
** note that windows is case sensitive so it might need to be "cd Windows"
ran cd system32
** note that system32 is case sensitive so it might need to be "cd System32"
ran mv utilman.exe utilman.bak
ran cp cmd.exe utilman.exe
reboot the computer back into Windows
At the login screen, hit Windows key + U
at the DOS prompt, run "net user USERNAME PASSWORD" where USERNAME is the name of the user and PASSWORD is the new password
** of note if you run just "net user" from a DOS prompt, you'll be presented with the existing usernames on the computer