1. How to Retrieve Lost PC Password on Windows 7

Windows Password Recovery Corporation is a top-rated Windows password reset tool, especially designed for PC beginners or green hands. We can use it to remove PC password without the old password or lose files. Just regain access to PC with a bootable CD/DVD/USB Flash Drive:                                                                  
Step 1: Download Windows Password Recovery Corporation and install it on an accessible PC;
Step 2: Burn its ISO image file into a bootable CD/DVD/USB Flash Drive;               
Step 3: Set PC with password locked to boot from burned CD/DVD/USB Flash Drive;
Step 4: Recover PC Windows 7 password to a new one.

2. How to Unlock PC Password Forgotten for Windows XP

In Windows XP, there is a default admin account with password blank. Sometimes, it may help us much! Now, we unlock PC password XP from safe mode:
Step 1: Press F8 key when PC starts;
Step 2: Select Safe Mode at Advanced Boot Options window, and press Enter;
Step 3: Click the Administrator account at the Windows logon screen;
If we have set this administrator password, the password should be input with the one set, or keep it blank.
Step 4: From Start -> Control Panel - user accounts -> Select the account password locked -> Input new password.

3. How to Remove PC Password to Windows Vista

At this time, we can try the Windows password recovery freeware – Ophcrack to help us remove password PC Windows Vista.
Step 1: Choose Ophcrack Vista LiveCD version to download and save its ISO file;
Step 2: Burn the Ophcrack LiveCD ISO File to a CD;
Step 3: Restart the locked PC with burned CD and launch to start cracking PC password.

4. How to Break PC Password with PC Password Reset Disk

PC password reset disk will be helpful for PC password breaker if we own it before we forget PC password. Now check the following steps from create PC password reset disk to reset password with it (Windows XP as example):
A. Start –> Control Panel -> User Accounts -> Select account to create its disk;
B. Select “Prevent a forgotten password” on the left of Related Tasks;
C. Prepare a blank disk and do as the following Forgotten Password Wizard. When the progress indicator displays 100% complete, click “Next” and then Finish.
D. Remove the disk from PC and keep it on a safe place.
Reset lost PC password with the created disk as steps:
E. Click the username at the Windows login screen and then press Enter when password box appears;
F Click use your password reset disk. The Password Reset Wizard starts and Next;
G. Insert the PC password reset disk, and then Next;
H. Input a new password in the Type a new password box and in the confirm box;
In the Type a new password hint box, we can type a hint to remind us the password if we forget the new password if we want to use one.
I. Click Next, and then Finish.

With the 4 methods, things will be easy if we lost password on PC and need change PC password. Now, efficiently to reset PC password and bypass the PC login admin password on Windows 7/XP/Vista!

Source: http://windowspasswordrecovery.net/article/forgot-pc-password.html