The first thing which you check if you forget login password. When we install Windows, it automatically creates an account "Administrator" and sets its password to blank. So if you have forget your user account password then try this:
 
Start system and when you see Windows Welcome screen / Login screen, press <ctrl>+<alt>+<del> keys twice and it'll show Classic Login box. Now type "Administrator" (without quotes) in Username and leave Password field blank. Now press Enter and you should be able to log in Windows.
 
Now you can reset your account password from "Control Panel -> User Accounts"
 
Same thing can be done using Safe Mode. In Safe Mode Windows will show this in-built Administrator account in Login screen.
 

If you happen to remember an older password that was used, you can restore the server's system state to a point where it had the old password.
 
Here's an article that talks about a few different methods for recoving administrative passwords: http://www.petri.co.il/forgot_administrator_password.htm

Offline NT Password & Registry Editor –This is a utility to reset windows password of any user that has a valid (local) account on your NT system. You do not need to know the old password to set a new one. It works offline, that is, you have to shutdown your computer and boot off a floppydisk or CD. It'll detect and offer to unlock locked or disabled out user accounts. It is also an almost fully functional registry editor.
 
HOMEPAGE: http://home.eunet.no/~pnordahl/ntpasswd/
 
Ophcrack – Ophcrack is a free Windows password cracker based on rainbow tables. It is a very efficient implementation of rainbow tables done by the inventors of the method. It comes with a Graphical User Interface and runs on multiple platforms.
 
HOMEPAGE: http://ophcrack.sourceforge.net/
 
These two tool are famous. but it will take some time and a little complicate.
more free windows password reset methods.