If you are comfortable messing with the Registry:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Authentication\LogonUI

Navigate to that Key and delete its content, OR rename that key to LogonUI.bak

That removed user will not show up in the last logged in list anymore;

I am not sure what you are referring to. It SOUNDS like you are referring to a BIOS password which would be completely unrelated to Windows or this article.

Alternately you could be referring to an old user profile that still exists in Windows even though you have deleted the files from C:\USERS. If that is that case, the solution is to remove them:
1: click the START button and type USERS
2: click on ADD EDIT OR REMOVE OTHER USERS
3: click on the dead user and select REMOVE

I hope that helps