Formatting Excel 2018

Having issues with formatting. I tried to insert a single accounting line in cells, but in order to do it I had to first choose anything but single accounting, then go back and select single accounting. OK, that;s a minor annoyance. The big issue is when using the sum() function - a cell was formatted to show a negative value with the minus sign, and no matter what i did, the minus sign would not show up. Only way to get it to show up was to drag another cell that was formatting correctly over it. Thoughts?