Method-1
Boot up with DOS and delete the sam.exe and sam.log files from
Goto:-
Windows\system32\configin your hard disk. Now when you boot up in NT the password on your bulit-in administrator account which will be blank. (i.e. that's was no password).
This kind solution works only if your hard drive is FAT kind.
Method-2
Step.1:-
Put your hard disk of your computer with any other pc.
Step.2:-
Boot that computer and use your hard disk as a secondary hard disk
Note:- Don't boot primary hard disk.
Step.3:-
Then open that drive in which the victim's window(or your window) is installed.
Step.4:-
Then Goto:-
Windows->system32->config
Step.5:-
And delete SAM.exe and SAM.log
Step.6:-
Now remove hard disk and put in your computer
Step.7:-
And boot your computer.
That's all completed.