URGENT: Why is my touch screen black but responds?

my 3ds has been in my cellar for quite some time. I took it out and everything apart from the forward cameras and my touch screen was fine. touch screen was yellow with black in the corners and camera doesn't work but I don't care about that at this time. after a while of playing, the lower LCD started to fade like an old tv being turned off. the black in the corners got bigger and soon covered the whole screen. the screen was black for ages and then all of a sudden when I turned it on once it went back to being yellow. then it went black again and has stayed that way ever since. it still responds but I cant see a thing.

can I just replace my lower LCD or will I have to buy a new one?

please help. I don't really want a new one.