Negative value causing issues

Hello all, i have what i thought would be a relativley easy problem to solve but i am struggling like mad with it. This is the problem. in Cell C3 i have 1158 and in Cell C4 i have 1163. C5 C6 C7 will when appropriate get numbers in as well. I want to subtract C3 from C4 and show the answer in D4 (the answer being 5 and being in D4) However when i continue the formatting down column D when i get a minus figure in D5 then the rest of the column is filled with zreos. That makes no sense so here is the sample from the sheet.
Any help please
Mike