Phone charges and holds charge but won't turn on

So after using the note 8 in my B-I-Ls pool (which turned out to be Saline and not Chlorine) the phone seemed to just die and has not turned on since.

It does however hold a charge, and the led light works, but I don't get any other feedback or function from it.

I have tried all combinations of button presses etc but all with no luck.

Is it likely to be the motherboard, amd does that mean all photos on the phone are gone forever?

Thanks for reading...

Steve