Problems Logging in Windows XP

I'm not sure if it was something I did or not, I have a
problems logging in when I'm at the Welcome Screen when I
first turn my computer on. When I click on any of the
accounts and want to type my password the white bar
that's supposed to appear to the right of the icon starts
to show, but doesn't completely appear, and it just
freezes. I tried Alt-Ctrl-Del, and it gives me the
normal login menu without the welcome screen, but it too
is locked. Eventually a pop-up window appears and says
something about the system trying to login and that it
wasn't able to do so.. but it finally gives me the option
to login. I tried to change the login screen settings,
but when I reloaded my computer it didn't even get to the
welcome screen.

I really don't know why I'm having trouble logging in and
using that welcome screen. I never had any trouble
before whatsoever. Now its frustrating me and I hope I
don't have to reinstall Windows to fix this problem.

-Rich