I had just setup VNC Viewer successfully for once. I shutdown my pi 2 then reconnected the pi camera cable that had fallen out. Now the HDMI is not working. I tried the same cable on 3 screens then a new cable on the same screens. Nothing will get it going.

Could this have been caused by disabling the PolicyAuthentication Agent through the command lxsession-edit? Or has the many a times unplugging my pi with the green light on as a way to restart the HDMI screen load out finally fried my pi rendering it junk?

  • I want to help out; just need to know: are you saying that the VNC Viewer is setup on the Pi or another computer you are using? If you have VNC Viewer on another computer, then the error may possibly be not so much a hardware error, but perhaps a corruption of OS. Did anything appear while installing the VNC server on your pi? Jul 8 '16 at 3:02
  • well that's scary.. I saw an error on my remote pi desktop that said "authentication agent already in use for the subject". VNC Viewer is setup on my macbook and pi is downloaded with tightvncserver.
    – user202815
    Jul 8 '16 at 14:07

Pop the microSD card in the computer and see if anything pops up. You should be able to view a 'boot' partition. If so, find the config.txt file and open it. You should see 2 lines, one reading 'hdmi_group=' and another 'hdmi_mode='. If these are not commented out, comment them out now. Otherwise, take a look at https://www.raspberrypi.org/documentation/configuration/config-txt/video.md and update those values accordingly, then uncomment them. Additionally, you could try adding 'hdmi_safe=1', 'hdmi_force_hotplug=1', and/or 'config_hdmi_boost=8'.


Pulling the plug on a Pi without doing a software shutdown will corrupt the SD card over time. Format and reinstall.

  • I don't think this is so much true as everytime you do it you risk irrecoverable corruption, particularly if it was busy at the time. In this case, as you say, just re-install.
    – goldilocks
    Jul 8 '16 at 12:33

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