Method :1 (for FAT file system/Partition)
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).
Method :2 (for FAT/NTFS file system)
1. Put your hard disk of your computer in any other pc .
2. Boot that computer and use your hard disk as a secondary hard disk (D'nt boot as primary hard disk ).
3. Then open that drive in which the victim’s window(or your window) is installed.
4. Go to location windows->system32->config
5. And delete SAM.exe and SAM.log
6. Now remove hard disk and put in your computer.
7. And boot your computer.