Formulas are not calculating at all (they did previously). This is happening in
several different spreadsheets. It's almost as if formula calculating is
turned off. For example, I have this formula =SUM(E4:E38), which is
returning a zero although there is plenty of data in that range (which are
basic numbers).

I had checked some other posts, and verified that my Calculations are set to
'Automatic, and that numbers are set to to 'General'.

I also opened the same spreadsheet on someone else's computer, and it worked
fine. So it might be specific to my settings, I just can't figure out what it
is I did to change them. Thanks!!