This trick will lead you to break the windows 7 without any extra tool or device.It only requires the general installation CD..
Start your computer and enter into Bios Setup. Change your boot preferences to boot from CD /DVD. Insert your windows 7 Bootable CD and select the “Repair your computer” option from the lower left-hand corner.

press SHIFT key 5 times.
That’s all there is to it. Now you can login with the password you entered now.
Start your computer and enter into Bios Setup. Change your boot preferences to boot from CD /DVD. Insert your windows 7 Bootable CD and select the “Repair your computer” option from the lower left-hand corner.
Once you been into repair mode select the command prompt option.

When you see the command prompt it's Bingo for you.
First you’ll want to type in the following command to backup the original sticky keys file:
copy c:\windows\system32\sethc.exe c:\
Then you’ll copy the command prompt executable (cmd.exe) over top of the sticky keys executable
copy c:\windows\system32\cmd.exe c:\windows\system32\sethc.exe
Now almost 90% of your work is complete.
Restart Your computer and remove the installation media(pendrive or cd whatever you inserted)
Start up normally.
When you get the log in area
press SHIFT key 5 times.
You would get a command prompt. Now type the command 'net user' without quotes. It will show you the available user accounts in the computer. From the list you choose the User whose password you want to reset.
For my case Nasim is the user whose password i wanted to change.
For changing the Password of any user type the command 'net user username *' without quotes where username reflect the name of the user.
For this case command becomes 'net user nasim *'
When you execute the command it will ask you to type a new password.
once you enter a password you have to re-enter it for confirming.
That’s all there is to it. Now you can login with the password you entered now.