System boots up without asking for login/password

I installed Windows 2000 professional with the login option as "System
assumes you are the only user who will login....etc. etc." (I don't recall
the exact wordings).
Now when I start the windows the system does not ask me for login and
password and it boots up without the login/password. But when I lock the
system and want to login again, I have to enter the password. I want the
system to ask me even when I boot it up the first time. Otherwise, even if I
lock the system, anyone can just turn the power off and turn back on and
enter the system without login/password. Please help me how I can force the
system to ask for the login and password when I start (boot up) the system
first time. I don't want to re-install the system since I have already
installed many software, service packs, security updates etc.

Thanks.....
.

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