How do i get the pop up to appear with the graphics and form in it? Not just being a blank pop up wi

When I use the pop over plug in all that shows up (and only SOMETIMES. I've tried on several different computers and browsers and it doesn't always show up, even if that's the first time I've been to my website on that computer.) If it does show up it shows up with a green background and only small text. None of the graphics or other things, and not the actual email form.