Black Screen and Scroll Problem

You're either having a spreading corrosion problem from the water, or it's not all dry in there and it's spreading, and the conductivity of the water is screwing up the circuits.

Open the camera as much as you're willing to risk it, and you're going to have to take a chance either way - either you take it apart, expose the boards, and every separate part with some distilled(non conductive) water (if you just dip the whole thing you'll have water caught in places) then put in an airing cupboard to dry for a week, thus taking the chance of causing more damage by not being able to reassemble it properly, or by causing more water damage, or you have another option of just opening all compartments -cards, battery - taking everything out and leaving it to dry, hoping that it will be enough. The chance you're taking here is that it's really a corrosion problem and you'll be helping it set it.

If you don't like both option take it to a repair shop.

Good luck