Nikon D3100 Black Screen Issue?

I'm having issues with the monitor display. I'm wondering if it had anything to do with a cord I plugged into an outlet that plugged into the camera's AV out slot because I got a little curious the other day.

Pretty much everything on the camera works fine such as the flash, changing of picture settings, shooting pictures and some other things. But when I switch to video I see in the view finder it's saying error on the bottom. I hear it switch to video mode but switch immediately back. So essentially the camera works fine except for the monitor is blank and the video mode doesn't work.

I'm thinking it may have something to do with the source of the camera, as I plugged a AV cable into it, and I'm just thinking it may think it's still plugged into another device so the monitor doesn't want to display. But I pretty much have no idea, that's just my assumption. I'm shooting a feature length documentary in about 3 weeks and I was gonna use this camera, Please help as it's incredibly important.

When was the last time you formatted your memory card?

You do need to shoot video with the camera unattached to any external device.

What you seem to be trying to do is tether your camera while in the video mode.

There are only a few cameras that can do that. Most notably, the Nikon D600, D800 and D4.

The AV connection is used to view existing video and still images. NOT for tethering.