Access tables do NOT work like Excel spreadsheets. You cannot perform calculations the same way. You cannot store data the same way. Access tables, though when open look like a spreadsheet, are not and you cannot refer to a field as you would a cell in Excel.
To convert a spreadsheet to Access is NOT as simple as dropping it in, you must learn relational design, you must learn database normalization. You must also understand that the tables only function is to hold the data. Everything else requires code, queries, macros or some combination thereof.
That said, to get the results you want you would need to create a running sum query but off of properly set-up tables. While we can help you do all of that we would first need to start with your table set-up and you relationship diagram. (Side note, this is not a few hours... more like a few weeks to a few months to get working properly.)