You want to logon as administrator, but you don’t have the computer name. This can pose a problem in windows 7 for domain joined machines as the local pc name dos not show anywhere, as opposed to XP you could se the computer name in in the domain list!
By default windows will have you log on to the domain, meaning that if you need to logon as the locale Administrator, you will have to type the pc name first, like this:
PC001\Administrator
Instead you can just type in a period, as that will resolve to the name of the computer, like this:
.\Administrator
It will of cause also save you the time I takes typing in the entire pc name.
