It happens to almost everyone at least once. You boot up your legacy machine, the familiar Windows 7 startup chime plays, and you are greeted by the login screen. You type in your password—the one you have used a thousand times—and see the dreaded message: "The user name or password is incorrect." Panic sets in.
Unlike other methods that blank the password, Ophcrack actually recovers it using rainbow tables (precomputed hashes).
This is the legendary free utility that works on everything from Windows 2000 to Windows 7. It works by blanking the password hash in the SAM file.
Windows 7 installation DVD or a recovery USB drive.