There are several tools and utilities that can be downloaded to recover or reset existing password. These password reset utilities can either read the registry and rewrite the password hashes, or can brute force crack the password for any user account including the Administrators.

1. Offline NT Password & Registry Editor
   Available as bootdisk or bootable CD, Offline NT Password and Registry Editor works to change or reset password of any users on Windows NT 3.51, NT 4, Windows 2000, Windows XP, Windows Server 2003, Vindows Vista 32 and 64 bit. It can also detect and offer to unlock locked or disabled user accounts.

   Download:
   cd070409.zip (~3MB) – Bootable CD image and can be used to make bootable USB drive.
   bd050303.zip (~1.1MB) – Bootdisk image for floppy disk, not compatible with Windows Vista.
   sc050303.zip (~1.4MB) – Boot disk image for floppy disk with SCSI-drivers, not compatible with Windows Vista.

2. John the Ripper password cracker 
   John the Ripper is a fast password cracker based on dictionary attack with a wordlist currently available for many flavors of Unix (11 are officially supported, not counting different architectures), Windows, DOS, BeOS, and OpenVMS. Its primary purpose is to detect weak Unix passwords. Besides several crypt(3) password hash types most commonly found on various Unix flavors, supported out of the box are Kerberos AFS and Windows NT/2000/XP/2003 LM hashes, plus several more with contributed patches.

   Download: John the Ripper 1.7.0.1 for Windows

3. EBCD – Emergency Boot CD
   EBCD is a bootable CD, intended for system recovery in the case of software or hardware faults. It is able to create backup copies of normally working system and restore system to saved state. It contains the best system software ever created, properly compiled and configured for the maximum efficient use. Features are such as copy files from unbootable volume, recover master boot record of HDD, recover deleted file, recover data from accidently formatted disk and floppy disk. EBCD also includes function to change password of any user, including administator of Windows NT/2000/XP OS without the need to know the old password.

   Download: EBCD Lite 0.6.1, EBCD Pro 0.6.1 

   Both contains necessary NT password recovery feature.

4. Ophcrack 
   Windows password cracker using time-memory trade-off on LM and NTLM hashes based on rainbow tables and supports Windows Vista, XP, 2003 and NT. This tool allows you to retrieve existing password.
5. RainbowCrack 
   Crack Windows password using time-memory trade-off cryptanalysis based on rainbow tables. Unless you already has dumped the hash for your Windows password, else this utility is for hacker as it provides no way to retrieve the password hashes when you unable to access to your computer.
6. L0phtCrack (LC5) 
   L0phtCrack (now known as LC5) is a password auditing and recovery application by using dictionary, brute-force, and hybrid attacks. originally produced by Mudge from L0pht Heavy Industries, and was produced by @stake after the L0pht merged with @stake in 2000. Support and sales has been discontinued by Symantec from end of 2006, after it acquered @stake in 2004. So you probably need a crack that lists below. If you unable to sign on to your computer, you probably can’t use this.

   Download: lc5-setup.exe (14 days trial)

7. Cain & Abel 
   Cain & Abel is a password recovery tool for Microsoft Operating Systems. It allows easy recovery of various kind of passwords by sniffing the network, cracking encrypted passwords using Dictionary, Brute-Force and Cryptanalysis attacks, recording VoIP conversations, decoding scrambled passwords, recovering wireless network keys, revealing password boxes, uncovering cached passwords and analyzing routing protocols. The program does not exploit any software vulnerabilities or bugs that could not be fixed with little effort. It covers some security aspects/weakness present in protocol’s standards, authentication methods and caching mechanisms; its main purpose is the simplified recovery of passwords and credentials from various sources, however it also ships some “non standard” utilities for Microsoft Windows users.This tool needs to be installed, so you must have another working computer to recover your password remotely. Thus it’s likely to be useful for system administrator only. Supports Windows Vista.

   Download:
   Cain & Abel v4.9.2 for Windows NT/2000/XP
   Cain & Abel v2.0 for Windows 9x