errors in formulas

[Penrhos]

I have a huge worksheet where I have been editing and changing some content.
I cannot get results to show properly.
Example: Column is 120 rows long, one row (35) has a value of 3,500. When
I use "=sum(B1:B120)" - in spite of the fact that B35 is 3,500 - the total is
0.
This is happening all through my sheets - it driving me nuts.

 

[Gary''s Student]

If the sum function shows 0, the data is probably Text rather than numerical.
(they may look the same):

1. clear an un-used cell (both format & value)
2. enter 1
3. copy the cell
4. select the data cells to be fixed
5. Edit > PasteSpecial > Multiply