LV issue

I did something; I don't know what, but now I only see a black screen with a red rectangle and a single red dot in the middle of it on my monitor in LV. I also see f stop and exposure and all that info, just can't see what I'm shooting at all. I've poured over my manual, books and internet trying to figure out what my problem is, but can't. I'm so frustrated. Can anyone help? This is my first DSLR, first Nikon, first really good camera and all my friends shoot Canon and just roll their eyes every time I get stuck. Thanks

Remove the lens cap.

EDIT: Sorry couldn't resist, hope you get it sorted out.

The red rectangle is your focus box. The red dot in the middle means that you are at the center of the viewfinder (if you are anywhere else, clicking the OK button on the scrolling button will move you there). Clicking on the + and - buttons should zoom you in and make the box get bigger and the dot should go away. If that's all you're seeing, pressing the info button should give you additional information and grids along with the red box.

Not sure why you have a black screen. Lens cap? I'm guessing not. Can you take photos or is the shutter locked? I found this issue after a Google search, but I don't think it's the same thing you're getting.

Does what you are describing look like this?
(first try - so if blank, not intended!)

Live view on the 600 and 800 reflects what you see based on aperture and shutter settings. If you set a small aperture and fast shutter in manual mode you get a black screen. In PAS modes it should be ok. Just a thought.

Assuming you don't actually have the lens cap on, what mode and aperture are you at? The D600 LV is terrible in that it won't change the exposure in M mode if you change aperture. If you are on a small aperture, change to A mode, try putting the aperture on the lowest number you have on your lens, then change back to viewfinder and back to LV, see if that helps anything. The LV on my much cheaper Canon DSLR (550D) is better than the D600 to be honest...

I think Geoffc may have touched on the heart of the problem (assuming it's not a lens cap). Toss the camera into P mode for giggles and see if you get something that's not black.

I tried switching from M to P, no difference. I noticed today that right as I turn a studio light on the LV screen lights up perfectly, but literally for only 1 sec, then turns dark again. I tried to use the screen brightening function using the slider on the right, but that didn't help much. I was just using it a couple of days ago and it worked fine (well it's inferior to my boyfriends Canon, but that's another issue)
BTW the lens cap is off, but that does sound like something stupid I would forget.
I'm using 4 125 watt equivalent LED lights, defused, 1/4 sec., F 20, ISO 100. Shooting Glass.

Just played with mine for 10 minutes. The only way I could come up with anything close to it was by bringing the Exposure Compensation down to -5 and dimming the display to -5, and adjusting WB brightness (hold the WB button down and use the down direction on the control wheel). Still, even with all that, if I aim it as something bright it shows up.

Does the display function normally the rest of the time?

I can see playback just fine. Thanks for your help!!!

Figured it out. I held down the exposure button while turning the command dial. Brightened it right up. Yippee!!! Thanks everyone for your help. I'm so lame.