Unhappy [q] htc hd2 problem pls help

Hi i am new here .. well i have a htc hd2 device .. and i tried to install android 4.1.2 jellybean with a guide from youtube but when i completed the first step my photo just open and i close it so i can continue the steps .. but when i tried to connect it at my computer i press volume down and power and nothing happened .. i tried everything to open it and nothing can smone help me? (sorry for my bad english)!