Excel problem

I downloaded a Excel "statement of account" that I could use to make monthly bills for our neighbor that we feed heifers for. It's great, it adds as you input the items. However, when I went to start the billing for January (Dec. was the first time I'd used it) it won't add in new item sums to the total as I enter them. I copied the Dec. form to a folder on my desktop, then after I was SURE it was in there, I deleted all entries from December, entered the balance from the Dec. statement as the "beginning balance" to the January one. I made an entry today for some salt blocks and it won't add to the total. What am I doing wrong? It is an "xltx" document. Maybe I'm just not doing something right to get it to work like it did the first time. I'm pretty obtuse on some of this stuff.