I had a HP elitedesk 800 G4 and I try to install ZimaOS and when I tried to boot with the USB key, I had the message Selected Boot Image not autheticate, Sure Start Bios is desactivate and USB boot was choose?
Thank
I believe your HP EliteDesk is blocking the ZimaOS USB because Secure Boot is still active in the background. Even when it looks disabled, HP SureStart can keep enforcing signature checks, and ZimaOS uses a non-Microsoft bootloader, so the firmware refuses to authenticate it.
I suggest checking the following in BIOS:
Disable Secure Boot fully
Enable Legacy Boot or CSM if available
Set USB Hard Drive at the top of the boot list
Save, reboot, then press F9 and pick the USB manually
I think once Secure Boot is properly off, the ZimaOS USB will boot without issues.
Than you
I will try that, hoping it’s will work
Disable Secure Boot fully —> I did that
Enable Legacy Boot or CSM if available —> I don’t have this option
Set USB Hard Drive at the top of the boot list —> I did that
Save, reboot, then press F9 and pick the USB manually —> I did that too
And I have the same message, it’s seem that the secure HP start is always there.
I made a test with an HP Elitebook and I am able to boot with the Zimaos usb drive, so the usb drive is ok. I don’t know if there is a way to bypass this problem with the HP elite desk. I have 2 HP Elitedesk, one is a G2 and the other is a G4, and I have the same problem whit both of them and they don’t have the same BIOS version. Maybe it’s because they are design for business computer?
Finally, I found the way to install ZimaOS on the HP Elitedesktop after many trial am it’s seem to work well. Now I’m learning to use it.
Do you mind sharing your way with the community here, so others can learn from it?
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I’m not in expert in BIOS, it’s probably why I took a bit of time to find out the solution.
First in configuration Bios 
Security: I disable alt item of HP security boot
In Advance menu:
In boot option I choose USB storage boot
In the bootom of this page in the list of booting device I disable all disk except the USB disk
in secure boot configuration In the scroll bar I choose Legacy support an secure boot disable too
I quit the menu and save the change.
I had to confirm by typing the number show in the screen to confirm change. If you a keyboard with a number pad, you must use it by activate num lock
I boot the pc again by using F9 to access to the boot menu and choose the usb,
there is the site of the booting meu for this computer.
Hoping the explaination are clear
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I believe the only reliable way to make the EliteDesk accept the ZimaOS USB is to unlock the hidden HP “Legacy Support” switch. On these business-class models, that option doesn’t appear until a BIOS Administrator password is created. Without that password, HP keeps parts of Secure Boot active even when it looks disabled.
I suggest setting a temporary BIOS Administrator password, rebooting back into BIOS, and then checking the Advanced > Secure Boot Configuration page again. On many EliteDesk units, the “Legacy Support and Secure Boot Disable” option only appears after the password is set.
I think once that hidden setting becomes available and is applied, the machine will finally boot the unsigned ZimaOS USB the same way your EliteBook does.
If that option still doesn’t appear after adding the admin password, then the firmware might be enforcing enterprise security permanently on that specific revision. Let us know what you see after creating the password.