Opening Screen

From out of the blue, one day last week, when I turned on my computer
the opening screen had a Circle with an X and "the user name or
password is incorrect" and below that was a box with OK in it. I click
on the ok and a second screen appears with three user icons. Two are
identical with same name, the other is the Administrator. The newer of
the user icons wants a password which I have never installed and can't
open, the other user icon I just click on and it opens. Curious where
this new opening page came from, where did the "user name or password is
incorrect" come from and how to get rid of it and the other icon on the
second page. Whew! Thanks in advance.

I also agree with others that this is my computer, I'm the only one that
uses it and I am tired of the UAC coming up each time I try to open
something from the net. I turn it off in control panel and it keeps
coming back on.

tjenkins