Is this DB shared or are there multiple copies on users computers?
Basically, you could have a table that you have one value in that you increment. Have the DB open a form that is not visible that will do this. Then have that form open your main form.
Or, create an update query:
UPDATE Table4 SET Table4.Field1 = [Field1]+1;
that runs from your Autoexec Macro that will run the query. Be sure to use the SetWarnings to turn messages both off and on.
There are many ways of doing this as more ideas are sure to be added to mine.