[wreck]

Ran into this with my Wife when we moved her to a new Laptop. We installed the latest version of all of her addons (over 50). Newest version of nUI+ etc. When she logged in her screen looked exactly like the OP.

What we did to fix it was log her out and disabled nUI only. She logged back in and we saw the regular Blizz UI. Logged back out and enabled nUI. Re-entered the game and everything was working.

So at least in this case by simply disabling and re-enabling nUI we got her back up and running. Faster and easier than disabling all of the other mods. At least in our case that's worked in a couple of cases. YMMV

Of course, this won't help people who are on an old version of nUI.