I know this is way late on the thread, years, but in case anyone else ran into this problem like i did and is scowering the web trying to find a solution I stumbled upon one. If your htc, or really any android if you can find the right update, this will let you reboot without the buttons. find a update or app that requires a reboot. that simple. For the HTC one m8, i know the lock screen security update calls for a reboot and promts you upon install if you would like to reboot, do it. I hard reset it first, and then found this out on updates, but you can always go into app updates and unistall the lock screen update and re-update it. How you get to the list of updates, go to play store, then click the menu and tap my apps & games, i scrolled down the list til i found HTC Lock Screen, clicked uninstall. it uninstalled, then asked if wanted to reboot, click yes, then it reboots. you can go back to the update and reinstall it, probably with another restart. its a little complicated i guess but its a work around. If you dont have a HTC maybe a google search will help you find a app or udate that requires a restart. let me know if this helped anyone.