Holding power for 10 seconds (and any of the combination with the volume buttons) did not help.
And when you connect it to the power does not even had the red led indicating that is charging.
If you connect it to a PC you get prompted to install the QHSUSB_DLOAD drivers.
So the phone is dead but not really completely dead.
Clearly that QHSUSB_DLOAD is a Qualcom hook that could be use to debug and probably re-flash the phone. The question is what is this tool and how do you use it?
I think there is some sort of standard way to recover across phone (maybe not all with a Qualcomm but I am sure that the protocol is the same among a few processors).
There are a few examples out there:
[UNBRICK] HTC Unbricking Project - http://forum.xda-developers.com/show....php?t=1627886
DLOADTool - https://github.com/posixninja/DLOADTool
And a lot of info about HTC internal here: http://tjworld.net/wiki/Android/HTC/Vision
So I wonder if anybody here has some idea about the tools and how to use to resurrect HTC phones and in particular the HTC One (M7).