Maybe this is due to the enumeration order, and the Pi is trying to boot from the first disk it finds.
i.e. when both are connected it's finding the HDD first, and trying to boot from that.
Try switching the USB ports the two disks are connected to?
The flashes indicate the problem.
Long Short status
0 3 Generic failure to boot
0 4 start*.elf not found
0 7 Kernel image not found
0 8 SDRAM failure
0 9 Insufficient SDRAM
0 10 In HALT state
2 1 Partition not FAT
2 2 Failed to read from partition
2 3 Extended partition not FAT
2 4 File signature/hash mismatch - Pi 4
Lots of mis-information here.
Logging in as root on the GUI for any purpose is valid on your own system
quote "Debian does NOT have a root login (for good reasons) but there should be no need to ever login as root."
Answer - simply untrue, Debian, ubuntu, Redhat etc etc all can be configured to log in as root on gui
Quote "No distribution ...
In general, when you do not have access to the Pi, the only solution is take the card out and mount it on another computer. On a Linux system, that is the easiest, and you may consider using a USB-booted Linux box for it (if you're on Windows).
First step after mounting the second partition of the SD card is to examine the logs. Normally, there should be ...
Time is the enemy of all tutorials. Windows 10 doesn't ship with the necessary RNDIS driver. You'll have to install it manually. See https://www.factoryforward.com/pi-zero-w-headless-setup-windows10-rndis-driver-issue-resolved/ for a guide.
menu bar is not available
when I start the GUI from root.
I have the same problem.
The wise guys taking care
of us stupid people.
"Simple answer is 'Don't do it."
That is not an answer
it is an excuse
"Debian does NOT have a root login"
"No distribution allows root to use a GUI"
Not true. Stretch has it.
Open a new ...