Could you send us a private message with your full model code and serial?
I Have same issue. But I found a way to turn on watch.
1. Charge watch
2. Remove watch from charging tray.
3. Place watch on charging tray again
4. When screen turns on and shows battery level, press and hold power button until watch turns on without removing wstch from charging tray.
You may need to repeat process 2, 3, and 4 for a few times.
Happened to me also. Just got mine last December of 2018 as a gift, so out of warranty. I was able to turn it on, but all sensor gone( step count, heart rate monitor...etc), it is basically just a watch. Then after 2 days it went dead completely and can't turn it on again.
Can you send us a private message with the below information here: http://bit.ly/2GH8URL