Ms Access: open form from specific ComboBox value

Clarifications

I will guess as to your form names

In the shipper combobox lost focus event.

Write something like

if combobox.value <> "" then
call form.show
end if

If you wish to display a loading message or screen for long queries, you can do something like this.

if combobox.value <> "" then
call load(formloading) 'load the loading message into memory
formloading.visible=true 'display it passively
call formloading.refresh 'refresh it to trigger a repaint, in the function "repaint" does the same thing
call load(form) 'Load the primary form into memory, any long queries in the load/initialize events will be done here
formloading.visible=false 'after loading, hide the loading window
call unload(formloading) '...and unload it
set formloading = nothing 'free up memory
call form.show 'show our newly loaded window
end if

Substitute form, formloading, and combobox for the proper names of your controls.

Also I suggest buying yourself a VB or VBA textbook, or learning to use google, as this sort of thing would be taught in an intro to VB course.