How can I reset a PC if I forgot the administrator password?

Suppose you found a PC in a closet and you want to reset it, but you forgot the administrator password. What can you do?

There is an emergency reset button that you can activate like this:

• Turn off the computer.
• Turn on the computer, but while it is booting, turn off the power.
• Turn on the computer, but while it is booting, turn off the power.
• Turn on the computer, but while it is booting, turn off the power.
• Turn on the computer and wait.

After three failed reboot attempts, Windows goes into recovery mode and one of the options there is to reset the computer. One of the reasons for that option is to address this specific problem of finding an old machine that you forgot the password to, and you want to just reset the PC and start over clean.

Note that doing this requires physical access to the computer, so we’re still covered by Law 3 of the Ten Immutable Laws of Security.

Update: Clarified that this resets the PC and starts over with a fresh install of Windows, erasing any data that had been on the PC. This is not a password reset.