The calculation setting is determined by the first opened file within Excel (with Automatic being the default). The easiest way to ensure calculation is set to manual is to create or find your Personal.xls macro workbook, unhide it (Window>Unhide) and use Tools>Options to amend to Manual Calculation and then rehide Personal.xls and close down Excel replying Yes when asked if you want to save changes to Personal.xls.
Now when you reopen Excel, your calculation settings will be on Manual.