Apple Watch won’t power on

Hello

I just charged my Apple Watch SE (2) to 100% overnight and I saw the time and green ring on the screen while charging as usual. But, when I went to put it on, it would not turn on. I tried long pressing the side buttons for at least 10 seconds but nothing would work. Just now though, it restarted after just being on the charger. It did this yesterday as well but then after a few minutes it turned black again with still a full charge. Does that make sense?

Could you please help me?

Thanks.