hi,
Mine was not charging at all after powering itself down from lack of power. I left it connected to the USB cable trying to charge overnight and no success. Then i remembered a little trick I used to do when i was younger with alkaline batteries which was to put them in the freezer.
I kid you not, i put my htc one m8 in a zip lock bag and then put it in the freezer for no more than five minutes. Came back and took it out of the freezer. it was nice and chilled not frozen. Then i simply plugged it into the USB cable again that is attached to my computer and within 2 minutes the light started blinking again. It needed that little bit of power that the freezer gave it from contracting the battery with the little chill it did get.
prior to this i tried cleaning the usb port and every other top with holding power and volume down. try this at your own risk it just worked for me!