Ok, I had just finished installing OS X Mavericks and I was going to the set up process, when my computer freezed and kept on loading. it was like that for more than an hour. I decided to restart it. When I was in front of the login screen again, I selected my user and typed my password. I am 100% sure it's right, I've been typing it in all sorts of ways just in case I was doing something wrong but it just keeps on refusing it.