[FxChiP]

> One of them has never turned on. I have no idea what it's for. It has an icon above it that sort of looks like a piece of paper.

Totally off-topic, but have you happened to start a print job on your machine and look at that light on Windows? That's my closest guess.

[georgieporgie]

I think it might actually represent the built-in SD reader, which at least makes sense, though it's still useless to me.