ground issue

Hey folks, 2011 260 Sundeck here. having an electrical problem. Had marina service the boat (oil change, lower unit svc etc) before storing for the winter in heated storage. put two new batteries into boat this year. Discovered electrical problem. Here is the problem and all the observations...

I have a 1994 Sea Ray 230. Mercruiser 5.0L 201 HP version Came back from 2 weeks away from the boat (and 3 major rain storms) and turned the key, no response from the gauges, all gauges and not even a flicker, and the engine turns over fine but does not start. Before I left the boat ran...