I don't think it could be the display cable if the display is presenting a good picture. I would look more into the trackpad. Maybe restarting the computer to reset things. or if the trackpad is getting stuck causing the computer to think you are selecting something.
Upon dropping a phone in water.. it is important to take the battery out to let it dry out. Try a new battery, if that does not work then ISO alcohol with light scrubbing of motherboard may bring it back to life.