My Nikon D3100 video is DARK

As you can see photos are okay and that's without flash but my video is way darker (This a screen shot of the video: ) Please Help I tried changing the ISO and settings.

Either you haven't changes the settings enough, or the D3100 just can't do video at that light level.

Crank the ISO up to the max, open the shutter to the max (f/3.5?), max out the shutter speed according to the fps of the video. If you still don't get anything, then you've reached the limit of the camera.