Please can anyone help?

We have a workbook containing many worksheets which has formulas in it
picking up from cells within the workbook and other external workbooks but
the formulas are not updating. We have checked and the calculation is not
set to manual (we have tried setting to manual and recalculating by pressing
F9 but it's still not updating). The only way the cell updats is by clicking
in the formula bar but as there are 000's of cells to do this to I was
wondering if anyone had any ideas as to why it's not calculating?

Any help would be much appreciated!

Many thanks.

Rachel