Would not restart
MY watch has a black screen and does not make a forced restart when pressing crown and side bottoms
Apple Watch Sport 38mm
Hi
Try charging your watch (allow around 2.5 hours for a full charge).
If it does not turn on after that, try force restarting it again: press and hold both the side button and Digital Crown for around 10 seconds, until you see the Apple logo.
If it still does not turn on, contact Apple Support (mail-in service may be available) or make a Genius Bar reservation with a view to having your watch checked under warranty: