Windows XP needs my current credentials

Hello! I am having problems with my Windows XP. I keep receiving error on my Taskbar that says, First of all, I don’t know what does lock your computer means. Does it mean I have to lock my user account and then unlock it with a password? I did not put any password on my Windows account. Secondly, what credentials are needed? Can someone please share some knowledge and explain this to me? I also hope that I can resolve this.
“Windows needs your current credentials.
Please lock this computer, then unlock it using your most recent password or smart card.”
Thank you.
