I just got my new "refurbished" Macbook Air Rev. B from Apple today via fedex and I think I have a problem or I'm seeing things. It seems as though when I sit it on an angle like kinda in my lap but kinda tilted laying on bed it seems to dim down on it's own. The power cord doesn't have a loose connection, and in preferences I have it set to not dim down ever! So what is causing my display to dim down? (also I always have the power cord plugged in).