Thanks for your reply. It's not published yet. Wont be finished for a couple more months.

I'm using just the one computer and I've not changed the browser settings.
Im only viewing it as a preview to know that it's doing this with the pop-ups. But yeah, like I said couple of weeks ago it was working fine and looked just how I wanted it. even if I take the size of the pop-up down it still opens a new blank browser window to view it in. I don't get it!

It can't be anything to do with me inserting a background layer can it? That's the only major thing Ive done to the site apart from continuing to add pages.