There is a Cable that isn't plugged in that seems to be Part of the Fan. Maybe I needed to remove it and forgot to plug it back in
If it's a larger 4-pin molex/AMP connector (like this), it was probably plugged into a cable coming off your old PSU.
If it's a smaller 3 or 4pin connector, it was probably plugged into a fan header on your motherboard at some point.
Anyway, you may as well take the fan out and move it to the back of the case before plugging it back in, as if you have only one, that's the best place for it.