Is it possible to clear the NVRAM so the machine can boot from UEFI devices again?

[NotCory]

My ED800 G1 SFF currently have an issue where it does not boot to any UEFI devices, but legacy devices works fine. There's no error message when trying to boot; it just skips to the next legacy device.

The reason why NVRAM is the culprit here is because I previously installed Windows 10 Team (a special version of Windows 10 for the Surface Hub) on my machine, and it wrote some contents to the NVRAM to prevent the machine from booting any UEFI devices again.

Here's the video demonstrating this behavior in a virtual machine:

 https://cdn.discordapp.com/attachments/730486372808392804/865630752226148362/2021-07-16_18-26-59.mp4 

It shows that, by deleting the NVRAM file of the VM, the booting behavior returns to normal. So I'm wondering if it's possible to do the same to my ED800 G1 to fix this problem.

Please note that I've tired:

• Clearing the CMOS my holding the CMOS button on the motherboard while unplugged for 5 seconds
• Updated the BIOS from version 02.77 to 02.78

But neither of above fixed my problem. I also can confirm that the problem is not caused by improperly created boot drives, as I can use them to boot other machines in UEFI just fine.

[DGroves]

nvram on just about all systems is kept intact on power off by a small battery somewhere (cmos battery)

shutdown remove power cord, then press power on button for 8 sec to drain motherboard caps 

now on motherboard find the cmos battery and remove it, once cmos batt is removed locate the cmos reset jumper or button and either jumper reset pins or press button for 5 sec

reinstall cmos battery and if using cmos reset jumper move back to normal operating pins, then power on enter bios and set date/time (make no other changes) power off then on and re-enter bios and see if legacy/uefi options appear and can be toggled

[NotCory]

Legacy/UEFI options are always here, and your solution of removing CMOS battery and resetting it doesn't work. It still skips UEFI and goes into legacy boot.

[DGroves]

when you cleared the cmos, were you prompted to reset the date/time? if not cmos was not fully cleared

[NotCory]

It did asked me to set date and time, but even after setting them up and allow UEFI booting, the problem persists. Forcing UEFI only also causes "No option to boot to." message appear.

[DGroves]

i don't think it's a nvram issue as a cmos reset by battery removal erases all stored settings and forces the system to use the system default cmos settings