Hi All
If your 720 is dead (black screen) and you have tried to use the Nokia reboot tool and that has failed to recognise the phone.
If your volume down button is busted.......take the phone apart .Tiny star drive under the sim cover and a small pick ,remove the battery clip(plug) from the main board ,plug the charger in for 10 mins,unplug it and put back the battery clip...........worked for me after 1 week of trying to fix it.
Good luck