refreshing formulas in cells
 

Hello
I have a simple sum formula in Cell A2 that adds two cells "=sum(A1:b1)" for
example. For some reason when I change the numbers or add numbers to Cell A1
or B1 the result of the formula dosent change in Cell A2 unless I page down
and page up and then It shows the new total. Ive used formulas for years and
every time I made a change to a number you could see the result in the cell
containing the Sum formula right away even though I was in the same frame of
that worksheet. My Auto calculate is checked vs using manual calculation
under ToolsOptions. Im using Office 2000.
What causes this?
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He4Giv (Dick)