Simple formulas from Excel 2013 do not work in Office 365 excel

[lngCDN]

So I bough the O365 personal edition and opened my Excel document, originally created in Excel 2013 and to my surprise, even adding a new cell and changing the formula on the "sum" cell, it did not take and calculate that value! 

I read all the other forums about making sure that formula is automatic (it is), and type is not text (it isn't - it is custom)

for example, the original formula is: =(J1234+K1234-B1234)

I added a new value in the colum "L".. now it is:  =(J1234+K1234+L1234-B1234)

It did not add the value contained in L1234 :( 

Am I doing something wrong? It is a brand new installed and newly opened so I don't need to "repair" office 365 as it was the first time using it and already it is wrong.

Thoughts?

Thanks

[#2]

@lngCDN 

I'm wondering whether the "custom" type has anything to do with it. Why not "number"?

Anyway, is it possible for you to attach the spreadsheet with that errant total?

[#3]

You are doing something wrong, but that's not clear what exactly. In particular, is =(J1234+K1234+L1234-B1234) exact formula or part of something else, and in which cell do you enter this formula (e.g. in A1234)