You don't know your password? Try leaving it blank. Whose computer is it?
Talk to whoever installed the operating system, since it is at that point
that the installer must provide a password for the administrator account.
Or, if you have admin rights with the account you normally use, just reset
the password to the password of your choice.
In cmd.exe:
net user administrator cat
The administator would then enter "cat" as his password.
Ray at work
