Forgot your Windows admin password?

• This is a utility to reset the password of any user that has a valid local account on your Windows system.
• Supports all Windows from NT3.5 to Win7, also 64 bit and also the Server versions (like 2003 and 2008)
• You do not need to know the old password to set a new one.
• It works offline, that is, you have to shutdown your computer and boot off a CD or USB disk to do the password reset.
• Will detect and offer to unlock locked or disabled out user accounts!
• There is also a registry editor and other registry utilities that works under linux/unix, and can be used for other things than password editing. 

How to use?

Please read the walthrough and the FAQ before mailing me questions If you have the CD or USB, all drivers are included.
If you use the floppy, you need one or more of the driver floppies, too.

Overview

1. Get the machine to boot from the CD or USB drive.
2. Floppy version need to swap floppy to load drivers.
3. Load drivers (usually automatic, but possible to run manual select)
4. Disk select, tell which disk contains the Windows system. Optionally you will have to load drivers.
5. PATH select, where on the disk is the system?
6. File select, which parts of registry to load, based on what you want to do.
7. Password reset or other registry edit.
8. Write back to disk (you will be asked) 

Download 

Note: Some links may be offsite.

CD release, see below on how to use

• cd110511.zip (~3MB) - Bootable CD image. (md5sum: fe0d30a1c540ec6757e748c7c09e2e4f) use this
• usb110511.zip (~3MB) - Files for USB install (md5sum: 50ced8d2a5febe22199f99acec74e63b)
• cd100627.zip (~4MB) - Previous version CD. (md5sum: 6d80cdfbba97457e413f95a3554d9524) The files inside the USB zip are exactly the same as on the CD. See below for instructions on how to make USB disk bootable.

Source : pogostick.net/~pnh/ntpasswd/