i suggest you look at your TOOLS / OPTIONS and chose the CALCULATIONS tab,
you may find that you have the 'manual' option checked.
Change to AUTOMATIC - then close excel and reopen all your documents. You
may need to do this for each doc, but sometimes Excel has a 'funny five mins'
The Automatic/Manual setting of calculation is Excel-wide. This means that
it's either on for all, or off for all. Whether it is on or off is
determined by its setting in the first workbook you open in the session.