I have a Nikon d3100, and the video is quite dark. How can I fix this?

When recording video, i have changed the aperture in an attempt to fix this problem (which did not help), and the ISO is decided only by the camera. When zoomed out to 18mm on an 18-55 lens, it improves only slightly. Even recording in my bedroom which is adequately bright, it is hard to make out objects because of the lack of exposure. Are there any settings I may have missed, or is there an effective way to fix this problem?

To help you out you need to learn how the aperture, speed & iso work.
http://www.cambridgeincolour.com/...posure.htm

Once you know how those work with each other then it's time for you to learn how to read an exposure histogram.
http://www.cambridgeincolour.com/...grams1.htm
http://www.cambridgeincolour.com/...grams2.htm

You can also improve your result by buying a fix lens with a big aperture such like a 35mm 1.8, 50mm 1.8, 50mm 1, 4.

Usually lens with F3, 5 aperture are not very good inside, unless you're planning on doing long exposures.

You can try cranking up your exposure compensation.

http://www.althephoto.com

You will need to add more light when shooting video, just like the big boys do in Hollywood. The "adequate" light in your bedroom may be adequate for your eyes, but in photography and video, if falls far short

Here is a link that should help you with shooting video

http://www.learner.org/interactives/cinema/index.html