The lock is a setting. Try going to settings on your reader, without it plugged into the computer, and see if it will let you unlock it. Then you can plug it back into the computer. I've never had the lock on so I don't know if it gives you a password when you lock it, but if you can't get it, you'll probably have to use the "reset" bottom on the bottom of the reader, and that will cause any ebooks on the reader to be erased.
In the end I managed to get rid of the password etc. a trap for
inexperienced players! Now all seems to be ok.