If you're wondering how it got switched to "manual"......

Excel takes the Calculation mode each session from the settings on the first
workbook opened in that session.

i.e. If you saved Book1 with calc mode in manual and opened it first, calc
mode would be in Manual.

If you saved Book2 with calc mode in auto and opened it after Book1, Book2
would be in manual mode(Excel ignores the auto calc mode in this case).

If you close Book1 before opening Book2, Book2 will be in auto calc mode.

Confusing enough? <g

NOTE: if you are loading Personal.xls and its settings are at "manual",
change this to "Automatic" and re-save Personal.xls.

Gord Dibben Excel MVP

Over the past few months, I have found that several
different workbooks I use have had Auto Calculation
turned off. This is odd because I am the only person who
uses this machine and these files. I never turn Auto
Calculation off. In fact, it took me a while to figure
out how to fix it the first time. I have yet to
determine a pattern.

Has anyone else experienced this? Is it a sign of
something dire or just a little bug to be tolerated?