I had a somewhat similar experience. My transmitter was working fine, after 4 years and 300 dives on the same battery. I figured that, although I carry a spare battery around, since I was diving the Red Sea for a month, I would replace the battery. Put a new one in, and when I got on board the boat, transmitter dead. switched out batteries. Nada. Switched computers. Nothing. Looked inside the transmitter -- spotlessly clean, no corrosion. Between liveaboards in Hurghada, went to the Oceanic dealer there and they tried various things. Nothing. they said that I have to send it back to Oceanic (Pelagic) and that they have some sort of transmitter software that they can use to reset the transmitter or something. Bought a new transmitter there for $US 200! Thank you Dive Store! The moral of the story: Don't change your transmitter battery until you have to, travel with a spare transmitter or a gauge, and a spare battery.
