Can't get to BIOS config on B450 Aorus Elite

[itm]

In preparation for an upgrade to Windows 11, I have converted my Windows 10 boot drive (M.2 MVMe SSD) from MBR to GPT, using the mbr2gpt.exe Windows tool. I then tried to reboot into BIOS (B450 Aorus Elite, Ryzen 7 2700X), to switch to UEFI boot mode, but I cannot get to the BIOS as the machine keeps booting straight back into Windows. Disk Mgt shows that the boot drive is now GPT, but the next time I try a cold reboot it will fail, as I am unable to set UEFI mode in the BIOS.

In my Windows power settings I have fast startup disabled. I have tried doing Shift-Restart then selecting Advanced Settings...UEFI firmware settings. When I do this the machine begins to restart, I hear a beep but then nothing happens (I have waited up to 20 minutes). Both displays remain blank. If I then press the reset button it reboots straight back into Windows (I don't see the motherboard splash screen).

I have tried connecting one of my two displays to the on-board HDMI port (I have a ZOTAC GeForce GTX 1660 SUPER 6GB Twin Fan Graphics Card), but it didn't help.

If I press the reset button, then continually hit the DEL key while the machine restarts, the machine never starts - both displays stay blank throughout. I don't see the motherboard splash screen. I'm using a wired USB keyboard, connected to the front USB port.

I tried removing the CMOS battery, waiting 15 minutes, then replacing it. It didn't help - the machine still boots straight back into Windows (or fails to boot into anything if I press the DEL key during the restart).

Any ideas?? I'm running Windows 10 Pro 22H2. The CMOS reset jumper is really difficult to access, as it's buried under a load of cables. Removing the SSD would also be a pain, as it's blocked by the graphics card, so I'd need to remove the graphics card first.

 

[Orcvader]

Removing the CMOS battery should do the same as the reset jumper so I wouldn't worry about that. I highly suggest trying to remove the SSD though to see if it boots into BIOS with no drive.

 

[itm]

Thanks. In the end I bit the bullet and removed the SSD (and graphics card). Finally got to the BIOS.
I then downloaded an updated BIOS from the Gigabyte site (in case my BIOS had become corrupted), but could not get it to install using the efiflash.exe utility from the site. It took me several attempts to get the machine to boot to a DOS USB stick (I just got a flashing cursor on the first 5-6 attempts), and when I finally succeeded it told me that efliflash.exe was "not compatible with the version of Windows" that I was running. I eventually discovered the built-in Q-Flash utility in the BIOS, and after half an hour of working out exactly how to use it (it's not the most user-friendly of tools!) I finally got the BIOS upgraded.
It's definitely not a process that I'd recommend for anyone with limited patience....