Boot up with DOS and delete the sam.exe and sam.log files from Windows\system32\config in your hard drive. Now when you boot up in NT the password on your built-in administrator account which will be blank (i.e No password). This solution works only if your hard drive is FAT kind.
Step 1. Put your hard disk of your computer in any other pc .
Step 2. Boot that computer and use your hard disk as a secondary hard disk (D'nt boot as primary hard disk ).
Step 3. Then open that drive in which the victim’s window(or your window) is installed.
Step 4. Go to location 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 :-)