I've had a couple teachers come to me with gradebook issues this week with things not calculating or show up right. More often, it is an issue with not having your grade calc options set up right. Here is a screencast to show you how to fix it.
I had a teacher ask me if there was a way to hide or remove students who are no longer in your class. The answer is maybe. It depends on if they are officially dropped from your class and appearing as red in your roster and gradebook. If not, then no, you cannot remove them until they have been unenrolled from the class. If the student is showing up as red in your gradebook though, you can hide them so you don't have to worry about them. Here is a screenshot to help you do it: