Default [H] HTC One Unresponsive Home/Back 2cm

Hi, a person offered me an HTC One factory unlocked, but he told me that he attempted to update and after that the Home and Back buttons stopped working and starting from the bottom of the touchscreen up to 2cm don't work either. I don't know this guy, so i don't trust him, do you say it's a software problem? Or maybe relationed with harware problem or cause of a drop? Thanks!