I have a Lowrance LMS 337 that was working fine. I was running back through a little rough water the other day and it started flashing bright then dim and beeping so I turned it off. I got back to the house to check it out and it will not power back on. I unhooked the power wire and hooked it back up. I changed the fuse and checked the wires it all looks good but will not power on. Any suggestion?