I am running Ubuntu 18.04 on an old Acer Aspire e1-470p pc (with Intel HD Graphics 4000 Graphics processor) connected to a Viewsonic VX2703MH-LED monitor by HDMI.
I corrupted my boot options (probably by toggling UEFI and Secure settings in an attempt to boot Ubuntu Live ) leading to an inability to boot into either Win10 or my Ubuntu. I was able to partially resolve the issue by installing a new 18.04 version alongside my old 18.04.1. Previously my Viewsonic monitor was working with an HDMI connection to my Acer Aspire.
The details of my problems leading up to this point are here.
After installing Ubuntu alongside my previous installation, my PC boots well into the new install if the Viewsonic monitor is not connected, although still does not boot well into the old install. See above link for Train error.
However, if I boot with the Viewsonic monitor attached by HDMI cable, the GRUB interface appears on the monitor in large black and white screen. If I choose to boot, the screen monitor goes white with vertical stripes and then white with illegible black and white blocks of characters.
If I boot without the monitor attached, and wait until successful completion into Ubuntu, when I connect the Viewsonic monitor by HDMI nothing happens. My monitor does not detect any signal from the PC. (The monitor is working fine with my Raspberry Pi).