Screen Problem

My screen works fine for the most part, but sometimes it goes really dim. When I move the lid, it goes back to normal. What is causing it to all of a sudden go dim? I have Apple Care for my Mac, but I've installed a new hard drive and new RAM; does that void my warranty? Any advice on this matter is greatly appreciated.

RAM and hard drive swaps do not void your warranty. If your screen brightens itself simply by moving it, I would definitely be making an appointment to take it in. Sounds like this could be a bare wire short or a loose connection.