Sorry for the frustration Rayban. I recall your note of using 2003 but I don't think the behavior is any different from my 2007. What you are describing sounds like what happens when the form that is the subform is open in either design or form view, probably layout view also, when the main form is open. Here's the best I think I can lay it out for you.
If the main and subform is closed and you open the main form in design view, the subform should show in the subform control. If you click once on the subform control, an colored line (orange in my case) should appear around the subform as the control is now selected. If you then right click on that line, the resulting shortcut menu should start with build options, editing, alignment and more stuff, with properties (for the property sheet) at the bottom with 'subform in new window' just above that. If you hit it right, you can get to this menu on a right click, but I find it's more reliable to ensure the control is active first. If you don't have the subform open in any view, and do find the option in the shortcut menu and open the subform, the white area spoken of will be the result. The only way to get it back to the original view is to close both forms and reopen the main form.
Of course, this all assumes you have bound a form to the subform control.
If none of that helps, then I know of no where to send you for paid help. That being said, we're all volunteers here, so if there is an acceptable way for you to post your db (such as Google drive) I will look at it for the usual fee - free - and see if I can help you out. Unfortunately, this site doesn't allow uploads of workbooks or databases for some reason.