14 DAY TRIAL // If you have a Windows operating system and you find yourself locked out, Linux is there for the rescue with a very handy tool, ntpasswd.
ntpasswd can be described as an “Offline NT Password & Registry Editor” and it's a tool that can be used to reset the password of any user that has a valid account on a Windows system.
The beauty of this tool is that it works on any system from NT3.5 on up, even the latest Windows 8.1. Its developer says it will also work on 64-bit architectures and the server versions (such 2003, 2008, 2012).
This is how it works, according to it's maker: “Windows stores its user information, including crypted versions of the passwords, in a file called 'sam', usually found in \windows\system32\config. This file is a part of the registry, in a binary format previously undocumented, and not easily accessible. But thanks to a German(?) named B.D, I've now made a program that understands the registry.”
For the most part the system is fully automated, but you need to read the documentation very carefully as it can also ruin your system.
The ntpassw tool is provided under the form of an image, which can be written on a CD or USB. If this does work, the developer also provides other means of running this tool, from another LiveCD, like Ubuntu.
Please keep in mind that this tool can ruin your operating system, use with care!