why i can't login to facebook?

There is always an option available in case we forget the password in every site go to forgot password and input your email id they will send you your password there in your mail box hope i help

There were a few times that this thing happened to me. It was during those times when they were trying to do some site maintenance. I even got frustrated at one time when all of my office mates were able to log in and I'm the only one left waiting for my account to be back up and running. You have to wait for a few good hours before trying to log in again and see what happens.