2 Answers

See Microsoft support. This question is answered there > http://answers.microsoft.com/en-us/windows/forum/windows_7-security/i-forgot-my-password-for-windows-7-for-my-laptop/d3bb29fc-6533-4887-b266-604af142b8e2

Option 1. Recover Windows 7 Password Via Another Administrator Account
If you have another user account with admin privileges, including built-in accounts in Windows 7/Vista/XP, you can easily bypass other accounts' password using Lusrmgr.msc and Command Line.
Log on Windows 7/Vista/XP with your administrator account. Click on Start, type lusrmgr.msc in the Search box(Win7/Vista) or Run box(Win7/Vista/XP) and click OK.
When the Local users and Groups dialog appears, open the Users folder. Right-click your user account and select "set password", type a new password and click OK.

Option 2 Recover Windows 7 Password using CMD command line
Step 1: Logon your Windows as administrator(You also can logon Safe Mode with Command Prompt, pressing F8 when restart your computer, hit up/down key to choose Safe Mode with Command Prompt and hit Enter).
Step 2: Click on Start, type cmd in the Run box or Search box and press Enter.
Step 3: Type net user, all user accounts of your computer will be listed.
Step 4: Type net user "UserName" "NewPassword"(replace UerName and NewPassword with yours), press Enter, then the password will be reset as new one and you can logon Windows Vista with it.

Option 3. Recover Windows 7 Password with Windows Password Recovery Tool
Download this tool and burn it to a CD/USB on another PC, then use it to boot your locked computer to reset lost password offline.
If you would like to read more: http://www.windowspasswordsrecovery.com