Following happens since the update from 14.04LTS to 16.04LTS. After some time of keyboard/mouse inactivity the PC turn to "standby/sleep" mode (screens turns black) which is pretty normal. Since the update the PC does not want to wake up after moving the mouse of pressing keys. The screen remains black and there is not other way to work with PC then power off and power on again. Of course losing data of files which were open. Anyone knows how to change this setting?