Im having the same issue with my wifes apple watch. She rarely wears it and it had been off the charger the last time she wanted to wear it. She put it on the charger and left it there for a couple of hours. When she went to take it off the charger she noticed it would not turn on. She told me it wouldn't work so I tried charging it on my charger. I noticed that the "snake icon" would turn on for 5 seconds and then turn off. Then back on and back off. It does this continually and gets hot. So its clearly taking a charge but will not turn on. I have tried every single trouble shooting suggestion and took it to the apple store. They told me theres nothing they can do about it other than sending to out for repair. They told me it would be $200 to repair it because its outside of its warranty window. Now I see that battery replacement by apple is only $80. What the hell? This watch has hardly been used even the stainless case has Zero scratches.
Just leave it on the charger overnight (after you see that "snake" icon), still cannot turn on?