My camera "froze" once. Shutter stuck halfway. I was told to check/reload my memory card. The connection is unclear to me but that was one theory posed to me that I might as well relay since you said its not the battery or a leak in the housing. Hope your camera is still under warranty and already in the shop.
You should ask the guys here about first aid. What to do the second you suspect a leak or a dying camera. I can imagine the horror of that while still underwater, housing in hand