If you have set up your gradebook and started to enter grades, but notice the category totals aren't showing up, the problem could be the Drop the lowest grade setting. If you are dropping an equal or greater number of items than you have actually entered in the grade book, the category total won't show up. For example, if you set up a homework category in which the two lowest homework grades are dropped, the category total won't show up until you have entered at least three homework grades for a student.
To check this, go to the gradebook and edit a grade category with this problem: Gradebook → Categories and items → Edit (gear icon). Turn on the advanced view (Show advanced) and look for the Drop the lowest setting.
To fix the problem, either wait to set up the Drop the lowest setting to the end of the semester (or at least later in the semester) or tell your students that the category total will appear after more assignments are graded.