My 3 series Apple Watch won’t charge or turn on, and it’s shows a red exclamation point inside a red circle.

Try to force restart/reset,

1. Press and hold the Digital Crown and side button simultaneously
2. Keep holding for 10 seconds
3. You will see an Apple logo

If this doesn't work contact Apple, it's probably dead.

This is caused by a corrupted update file and is usually terminal;

If you see a red "!" on your Apple Watch