Excel App gets focus

[Steven]

If you have an excel file open and then switch to another applicaiton...then
select the excel file again on the taskbar ... how can you catch this and run
a macro with the change in application back to excel? I want a macro to run
each time the file is accessed. Whether going from an excel file to this
file or from a different application to this file. I have tried
Workbook_Activate ... but that only works from one excel file to another ...
it does not seem to catch the return to the excel file from a different
application.

Thank you for your help.

Steven