O Ubuntu não detecta mais a tela externa [fechada]

Question

Acabei de instalar algumas atualizações e reiniciei e depois disso o Ubuntu não detecta o monitor externo. Está conectado com HDMI. O que posso fazer sobre isso? Não aparece nas configurações de exibição. Eu uso um laptop e o monitor embutido está funcionando e detectado, mas o monitor externo parou de funcionar depois da atualização de hoje. O computador é um Dell Latitude E7450.

$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation Broadwell-U Integrated Graphics (rev 09)

~$ dmesg | grep -E 'VGA|HDMI'
[    0.882972] fb0: VESA VGA frame buffer device
[    5.718803] fb: switching to inteldrmfb from VESA VGA
[    5.719040] [drm] Replacing VGA console driver
[    6.224466] input: HDA Intel HDMI HDMI/DP,pcm=3 as /devices/pci0000:00/0000:00:03.0/sound/card0/input16
[    6.224530] input: HDA Intel HDMI HDMI/DP,pcm=7 as /devices/pci0000:00/0000:00:03.0/sound/card0/input17
[    6.224590] input: HDA Intel HDMI HDMI/DP,pcm=8 as /devices/pci0000:00/0000:00:03.0/sound/card0/input18



$ dmesg | grep -iE 'fail|error|skip'
[    0.000022] Calibrating delay loop (skipped), value calculated using timer frequency.. 5187.65 BogoMIPS (lpj=10375316)
[    3.285636] psmouse serio1: Failed to enable mouse on isa0060/serio1
[    4.077454] EXT4-fs (sda1): re-mounted. Opts: errors=remount-ro
[    5.849972] init: failsafe main process (612) killed by TERM signal
[    7.787412] systemd-logind[854]: Failed to start unit [email protected]: Unknown unit: [email protected]
[    7.787417] systemd-logind[854]: Failed to start user service: Unknown unit: [email protected]
[    8.418720] systemd-logind[854]: Failed to start unit [email protected]: Unknown unit: [email protected]
[    8.418725] systemd-logind[854]: Failed to start user service: Unknown unit: [email protected]
[    9.170491] vboxdrv: module verification failed: signature and/or  required key missing - tainting kernel
[   16.373837] systemd-logind[854]: Failed to start unit [email protected]: Unknown unit: [email protected]
[   16.373842] systemd-logind[854]: Failed to start user service: Unknown unit: [email protected]

$ xrandr
Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 32767 x 32767
eDP1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 309mm x 173mm
   1920x1080      60.0*+   59.9     48.0  
   1680x1050      60.0     59.9  
   1600x1024      60.2  
   1400x1050      60.0  
   1280x1024      60.0  
   1440x900       59.9  
   1280x960       60.0  
   1360x768       59.8     60.0  
   1152x864       60.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
DP1 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

Atualizar

O seguinte procedimento resolveu o problema: Inicialize o Ubuntu 14 ao vivo a partir de um pendrive. Em seguida, reinicie o Ubuntu nativo instalado e a tela externa funciona.