Greetings and thank you in advance for any help.

I have a workbook that is 671K in size and contains about 75 different
worksheets. The first tab is a summary and details are provided on the
remaining tabs.

The problem I'm having is that the summary sheet has stopped updating. The
formulas are simple (e.g. sum a row, show the contents of a cell, etc.).
Calculation is set to automatic but I've tried switching it to manual and and
still nothing.

The only way a cell will update is if I select a specific cell, F2 then ENTER.

Any help you might provide is appreciated.