I have a Dell Latitude 7480 laptop with preinstalled Windows 10.
I installed Lubuntu 20.04 on it, with dual booting.
Things worked fine until I tried attaching an external monitor (that worked perfectly fine with my ancient Lenovo laptop).
I discovered that with attached screen latop starts bootlooping. GRUB menu appears as usual and starts countdown from 10.
After 2 seconds (when it reaches 8) laptop screen flashes black screen, GRUB appears again but
- it stops reacting to a keyboard input
- continues flashing black screen every few seconds
- countdown freezes
- neither Linux nor Windows boots
There is no error message at all – so I have no good terms to google for and neither DDG nor Google nor asking on Lubuntu Support telegram channel helped.
As workaround I can remove HDMI cable, select OS in GRUB menu and reattach it (attaching too early freezes boot, but attaching it too late causes Windows to not detect monitor at all).
Using screen after boot:
- With Windows 10 it worked fine (except extremely annoying interface to change screen settings)
- Screen refused to work at all in Lubuntu until I installed Nvidia Drivers ( How to install Nvidia driver in Ubuntu 18.04? was still mostly applicable )
There is no error message at all – laptop screen flashes black after about 2 seconds of GRUB screen and it stops reacting to a keyboard input.
I am primarily looking for info what is the proper method of diagnosing GRUB issues, how GRUB can be updated safely and how can I get rid of this problem.
To avoid XY problem: yes, I need Windows OS. I need it to file taxes using some insane program distributed as PDF file that is not openable by anything on Linux (and even if I would find workaround for this specific file it will likely happen again).
Workaround: remove HDMI cable as system boots, attach it immediately after GRUB stage. Yes, it is ridiculous and I want to stop this.
More info: I never tried booting with monitor attached before I installed Linux (maybe problem was happening also while it was just Windows?). Problem is not happening with HDMI cable attached and not connected to an external display.