Excel Macros: Starting up and Exiting

I need to build a macro that will start as soon as I open the Excel file, do some processing, and exit Excel. What I intend to do is, schedule the Excel file to run at night, retrieve data from an Access database, save the file and exit Excel. I need to know how to automatically start the macro when the spreadsheet file opens and after it finishes it’s processing, save the file (with no prompt to overwrite the file) and close Excel. Thanks.