Could be several things.
First, do you have adequate power to the unit? I believe it's advertised as 9 to something like 35 volts, but mine used to shut off above 9 volts (as near as I could tell.) Good first step would be to measure the input voltage.
10 seconds, it has likely gone through at least some of its self-checks, and is possibly trying to load the basemap. If you look close, there will be a very thin status "bar" at the bottom that lights from left to right as it goes through all the checks. It finishes not quite all the way to the right, as I recall. If you have a card in the unit, remove it and see if that helps.
If it is failing one of the self checks, there's not much you can do but return it to Lowrance for repair. In the US, they have a flat fee repair price; last time mine had water get in they sent me a new unit.