Create a macro with the name Autoexec. This will run first when the application opens. The macro can either do your startup checks or call a VBA function which do what you want done before the application starts.
If you are wanting to restrict access to the backend file for your application, you would need to place the Backend file on a network location and restrict access to that network location to everyone except your database users. You could also pasword protect it and have your front-end file be able to access the data even with the password in place on the backend. This is a lot of hassel if you do have to do it. I would try the network restrictions first.