I'm sorry, I didn't clarify very well, it's not the border that's missing, I can get the nerfed/classic/hidden border styles to show, that's not the problem. The issue I'm having is the background is completely transparent. Like the background behind the target portrait, and mana and health bars. But it's just for the target frame.
Again, thanks for any help in advance!!
Edit: Figured it out, it was the Frame Colors setting in the Global Settings Menu. Transparency was set to 0