You can certainly try the procedure again while it is plugged in to the charger. I don't know if that will help or not.
Contact HTC when you are able to and maybe they will have some additional troubleshooting guidance.
It could just be that the battery isn't holding a sufficient charge for it to power on any more? Batteries definitely do fail. HTC can replace the battery if that is what the problem is, but I still think you will need to mail it to them for them to diagnose and then replace the battery.