Formula's not calculatin in Excel 2007

[Max]

Hi,
Earlier if i had formulae in excel , if i entered any value(for ex a10 was
sum of a1 to a8 and if i entered any value in a4 automatically a10 used to
show 4 ie) the resulting value cell used to automatically calculate as usual.

But now i am observing from few days that regardless of any excel i open ,
if i enter any value where formula exist the values are not getting
automatically calculated.
I have to manually go to the cell which has formula and when i double click
and press enter the formula works. This is happening for any sheet i open

Is it because that any settings have changed in Excel .
Please let me know
thanks

 

[Student]

Office Button -> Excel Options -> Formulas -> Ensure Automatic is
checked under Workbook Calculation