OK, a long shot and a guess. Open the unit to about 90 degrees and stand it on edge - this MAY help the moisture to escape from between the resistive layers and the screen. I say may because there is capillary action trying to keep that moisture there.
The other thing you should do is take off the plastic covers and check the battery contacts aren't getting corroded and there is no sign of water damage on the circuit boards and cable sockets.
From what you have written there is every chance that you unit will work again as it did.