Manter pressionado o botão liga / desliga é a única maneira de desligar meu Acer Aspire F5 - o problema veio com a atualização do Ubuntu 16 (depois de apenas 2 meses de experiência com o Ubuntu).
Este é o log de erros da inicialização:
12:26:33 bluetoothd: Failed to set mode: Blocked through rfkill (0x12)
12:26:26 gnome-session-b: CRITICAL: Unable to create a DBus proxy for GnomeScreensaver: Error calling StartServiceByName for org.gnome.ScreenSaver: GDBus.Error:org.freedesktop.DBus.Error.Spawn.ChildExited: Process org.gnome.ScreenSaver exited with status 1
12:26:11 bluetoothd: Failed to set mode: Blocked through rfkill (0x12)
12:25:52 gnome-session-b: CRITICAL: Unable to create a DBus proxy for GnomeScreensaver: Error calling StartServiceByName for org.gnome.ScreenSaver: GDBus.Error:org.freedesktop.DBus.Error.Spawn.ChildExited: Process org.gnome.ScreenSaver exited with status 1
12:25:50 wpa_supplicant: Could not read interface p2p-dev-wlp3s0 flags: No such device
12:25:48 NetworkManager: ((src/devices/nm-device.c:1452)): assertion '<dropped>' failed
12:25:43 bluetoothd: Failed to set mode: Blocked through rfkill (0x12)
12:25:21 kernel: nouveau 0000:01:00.0: bus: MMIO read of 00000000 FAULT at 10ac08 [ IBUS ]
12:25:21 kernel: acpi MSFT0101:00: platform device creation failed: -16
12:25:21 kernel: platform MSFT0101:00: failed to claim resource 1: [mem 0xfed40000-0xfed40fff]
12:25:21 kernel: [Firmware Bug]: TSC_DEADLINE disabled due to Errata; please update microcode to version: 0x52 (or later)