ToolsOptionsCalculation can be Auto or Manual.

Excel takes the Calculation mode each session from the settings on the first
workbook opened in that session.

i.e. If you saved Book1 with calc mode in manual and opened it first, calc
mode would be in Manual.

If you saved Book2 with calc mode in auto and opened it after Book1, Book2
would be in manual mode(Excel ignores the auto calc mode in this case).

If you close Book1 before opening Book2, Book2 will be in auto calc mode.

Confusing enough? <g


Gord Dibben MS Excel MVP

On Wed, 23 Sep 2009 09:39:40 -0700 (PDT), Eirann wrote:

I had this same problem and was able to resolve it by fixing the
calculation settings in Excel 2003.

Try: Tools Options Calculation and make sure the option is checked
for automatic calculation.

I hope that helps - it fixed the issue for me, although I have no idea
how it got changed in the first place. :)