What should be done with laptop freezing on boot iff monitor is attached - Dell laptop with Lubuntu 20

Question

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 G550 laptop with Lubuntu 20.04).

I discovered that with attached screen latop starts freezing and flashing screen. 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:

1. With Windows 10 it worked fine (except extremely annoying interface to change screen settings)
2. 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.
• Problem is happening with a different HDMI cable
• Happens with Philips 227E QHA 1920x1080
• yes, my old laptop currently has no GRUB (though it used to have one in past...)

Answer 1

This is a tough diagnosis problem. Some more info would help, as listed below.

In the meantime, and as listed in the sources below for related (although not exactly the same) problem, you could try these alternatives, perhaps in combination:

1. Reduce the timeout for booting to 1.
2. Set Recovery Mode as the default boot option.
3. Avoid the splash boot loader, using GRUB_CMDLINE_LINUX_DEFAULT="". See How do I disable the boot splash screen, and only show kernel and boot text instead?
4. Use nomodeset in the boot option in Grub. You could set it permanent for a while with GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nomodeset". See also How do I set 'nomodeset' after I've already installed Ubuntu?
5. Force booting from a LiveCD by setting the boot order and/or disabling the HD. This will give you a system where you can perform tests.
6. Force booting from an external HD by setting the boot order and/or disabling the internal HD. This will give you a system where you can perform tests. YMMV depending on what you have in the external HD.
7. Try determining if you have the correct graphic drivers. This is an unlikely source of error, as the problem is with Grub...

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Sources:

1. Boot freeze when using second monitor (Xubuntu 16.04)?
2. My computer boots to a black screen, what options do I have to fix it?
3. https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1559308
4. https://bugs.launchpad.net/ubuntu/+source/plymouth/+bug/1872159
5. https://ubuntu-mate.community/t/system-freezes-when-connecting-to-external-monitor/5825
6. https://www.reddit.com/r/linuxhardware/comments/hc0pzn/lenovo_p53_grub_hangs_with_usbcdisplayport_cable/
7. https://itsfoss.com/fix-ubuntu-freezing/
8. https://larryreznick.com/2019/05/07/forcing-an-external-monitor/

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Useful additional info:

1. What do you mean by "bootlooping"? Your description looks more like a boot freeze.
2. Monitor brand, model, resolution.
3. PC model and OS of your old Lenovo that was working fine with your monitor.
   Did it have Grub?
   Are you willing you install Grub on that old PC as a means of testing?
4. Connector you were using with the Lenovo.
5. Do monitor&Dell have another connection that may be tried?
6. Do you have another monitor or TV that you can try with your Dell?