There are four solutions for your problem.
Solution 1: re-install your windows 7 operating system.
Solution 2:unlock your password from Safe Mode .
step 1：Start your win 7 computer and press “F8″ while the computer boots up. Scroll down to “Safe Mode with Command Prompt” with the arrow keys on the keyboard and press “Enter.” Your computer starts in Safe Mode with Command Prompt.
step 2：Select the Administrator account that appear in the screen, then enter command prompt. Type: net user ****** 123456 and enter (****** is the account name and 123456 is the new password), it will show you a message that” the command completed successfully.
Step 3: Restart your win 7 computer, then you can log in as ****** with the password 123456. You can go to control Panel to change your account password if necessary.
Solution 3:restart your computer with windows 7 password reset disk.
Password reset disk only works on condition that you have created it before losing the account password.
Step 1: While typing a wrong win 7 password, a password hint will appear. Click “Reset password “, it will show you the Password Reset Wizard.
Step 2: Click NEXT and select your disk drive to reset the password with a new one.
Step 3: Then you can use the new password to log in your win 7 PC.
Solution 4:crack your windows 7 password with Windows Password Key
Step 1: Download and install Windows Password Key in another accessible PC.
Step 2: Run the downloaded file to install Windows Password Key Standard. You can install it on any PC you have access to.
Step 3: Windows Start menu - From your Microsoft Windows Start Programs menu, select Windows Password Key Standard, it will be launched automatically.
Step 4: Using a Windows Password Key CD/DVD to reset Windows password or using a Windows Password Key boot-able USB Flash Drive to reset windows password.