Running only 1 instance

[MKSa]

For the App.PrevInstance property to be true the same application should be invoked from either the application Full Path or shortcuts. Invoking a copy of the application will not fire the App PrevInstance. The code below should do what you asked for.
private Sub Form_Load()
If App.PrevInstance then
'Delete the following line after testing
MsgBox "Found Instance"
Unload me
End
End If
End Sub