Prior to this tutorial you will need to have some small knowledge of linux and already have it installed on a thumbdrive, click here to learn how to install linux on a thumbdrive.
The Linux Stuff
boot into linux (Ubuntu and Lubuntu work fine), open the terminal. type "sudo apt-get install chntpw" to install the tool. You will then need to find the directory of the windows SAM file. Navigate to "/media/YOURUSERNAMEHERE" and replace YOURUSERNAMEHERE with your linux username. Find the drive with windows installed remember the Label or name of the hard drive installed, then in terminal type "cd /media/YOURUSERNAMEHERE". In my case the drive with windows on it is called "Windows" so I would then type "cd Windows", from here on it is simple type "cd /Windows/System32/config" then type "chntpw -i SAM". Remember when you are typing directory paths linux is case sensitive, which means that "Windows" and "windows" could be two different folders or files. Once you have finished the following steps type "chntpw -i SAM" this will list all the usernames in the SAM file. Using the tool first renable the local Administrator account and blank the password for it. Then shutdown the computer.
The Windows Stuff
Boot into windows by removing your thumbdrive and turning the computer back on. To login put "Administrator" in the username box and leave the password box blank.