Troubleshooting my iWatch3

When I took my watch (iWatch 3) off the charge this morning, it was warm and the Apple logo was showing on the face. When I pushed the side button the screen went black. I have put it on a different charger and the Apple logo will appear and disappear. I have also held down both side buttons for 20 + seconds and got nothing but a black screen.

What is my next step?