Can't switch users: Message says computer locked

You all helped me once before and I'm asking for help again. I have four users on my computer. Suddenly I can't switch between them. When I hit start/log off/switch user, nothing happens. I saw the little message that said you can also switch by hitting windows key + L. Here's where I may have done something wrong. I hit the windows key and l at the same time and got a window that said "The computer is in use and has been locked. Only XXXX(my service tag#/Roy(my name) or an administrator can unlock the computer.'' Then is has my name in a user name box with a password box underneath. I don't ever remember creating any kind of password for any of these users. And I've tried all the usual suspects but got nowhere. At the moment, if my wife or kids or any of us want to switch users, we have to log all the way out of the current user and log in as the other user.
I've looked around the questions already asked, and though some seem a little similar, no one has the exact same problem.
Can you please help?
Thank you in advance.