Apple Watch SE wouldn’t light up from black screen and when a hard restart is done, flashes white and goes black again

I have been using my Apple Watch (brought end of Jan 2023) all day absolutely fine. Went swimming with it and got out at 10:15am, came out and emptied water etc and was working fine. Continued using it.

At about 5:15pm, I think ‘I haven’t felt my watch for a while’ and tap it into life, black screen. I’ve tried multiple hard restarts (pressing both buttons - on charge & off charge), and it flashes white screen but won’t bring up the apple logo.

I unpaired it from my phone and tried to repair - the watch is vibrating and making sounds but still only a black screen. Hard reset just flashed the white screen again but no Apple logo.

There is no damage to the screen and it has a case on it. However I do swim with it twice a week and have done so since first getting it 16 months ago.

Everywhere just tells me to try hard restart which isn’t working. Any recommendations?