The following information is from a SlashGeek article by the same name:
Reset Windows password with Linux in under 5 minutes
Posted on June 9, 2012 in Hacks, Linux, Microsoft, Under 5 Minutes by potatoadmin
Prerequisite:
You need a linux live CD, preferably Ubuntu live CD. Doesn’t have to be Ubuntu, it can be a custom linux live distro with the right packages (the ones we need) installed. And you need to have the ability to boot from CD. Which should be pretty straight forward.
Step 1:
Boot in to your live CD and install chntpw
Step 2:
Do cat /proc/mounts to get the label of your windows HD.
cd to your media label.
Now cd to to your system folder (windows 7): cd Windows/System32/config/
Step 3:
Change or reset windows admin password by running chntpw: sudo chntpw SAM
You will get a prompt and the options are self explanatory. For instance to reset password enter “1” and then “y” to confirm. To change password enter “2”, then your password, and “y” to confirm.
Done in 5 minutes (or so). This should work on all versions of windows since Windows2000.