Column will not Sum in Excel

I have a spreadsheet that was created by exporting an Access Query to Excel. I formated the cells as needed, currency for currency and such. I tryed to sum up the columns and I have some that will give me zero when there are value in the column. Some of the columns worked just fine and some do not. I inserted the Sum function by clicking the cell I wanted the value in and clicked the sum button and the ones that worked automaticly selected up the values I wanted to Sum, The ones that wouldnot Sum did not select up. If I select sideways it will Sum The values or if I enter in the range from on of the columns that did sum it will show the correct value. What could the problem be?