Are you trying to use System Restore or the Recovery Console. If you are
trying to use System Restore, it would only ask for an administrator
password if one had previously been set. Are you trying to accomplish this
on your own system?
Since it appears you didn't set a password but are receiving the message you
describe, I'm going to assume you actually are trying to get into recovery
console which will ask for a password, leave the password blank and press
enter. It's asking for the password to the system's hidden admin account to
which most users don't to set a password.