Microsoft works

First check the formatting of the cells, then check under file-preferences to see what works is programmed to do, if this gives no clue, you could easily create a copy to experiment on and on the copy, highlight the entire sheet, and clear all functions and formats, then experiment with your calculation, if it performs ok, you will know that there was something else going on in the original cells. Finally, instead of the auto-sum function you could manually put in the sum formula eg D2=sum ( A34:A57)
If all this fails, post back and we'll dig further......good luck