Unable to log on to xp!

Last night I went into the Control Panel and changed User info so that I
thought I would not need to type in a password and changed to only 1 user for
my computer. Mainly because my children are now off to college and it's only
me and my wife using the computer.
I don't remember exactly what I did, but I can not log onto xp. It has my
user name and I'm supposed to type in my password. Everything I have tried,
my previous password I have been using up until tonight, along with anything
I could think of........ the "logon message" tells me that "the system could
not log you on. Make sure your User name and domain are correct, then type
your password again. Letters in passwords must be typed using the correct
case"
Nothing has worked. Is there a way to log on, or changing my user name
and/or password so that I can use my computer???
Thanks in advance for your help.