Ah it was the password for the admin account and not the key!

Afaik you could just set a new admin pw using a livecd and some tool.

I wonder if that’s still possible.

Not only is it still possible, there's even a first-party tool to do so,

https://learn.microsoft.com/en-us/microsoft-desktop-optimiza...

This only works for local accounts, though similarly trivial techniques apply to AD accounts if you have offline access to a domain controller.

Just to be clear, in neither case is this a security vulnerability; under the original "live CD" assumption — specifically, that you're able to make arbitrary registry edits — there are simpler ways to bypass Windows security that require neither tools nor understanding HKEY_LOCAL_MACHINE\SAM registry hive.

For example, make the registry edit given by

  reg add "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\
  Image File Execution Options\sethc.exe"
  /v Debugger /d C:\Windows\System32\cmd.exe /f

Then, at any login, lock, or "Ctrl+Alt+Delete" screen, pressing the Shift key five times gives you a shell running as NT AUTHORITY\SYSTEM[1].

This has immediate effect — you don't even need to reboot or log out.

[1] https://learn.microsoft.com/en-us/windows/win32/services/loc...