MSI B550 Tomahawk + Ryzen 5800x: straight to Windows, no Access to Bios

Setting: I have a M2 drive that contains a Windows 10 x64 installation that was working just fine on an older system. This morning, that drive was dropped into a new system with

• a MSI B550 Tomahawk board (BIOS Version 7C91vA5, Release Date 2021-01-26)
• a Ryzen x5800 CPU

At first the new system would recognize the drive but would not boot. It would bring me to BIOS every time, until I changed the boot mode to CSM. Then it would boot to Windows, which I used to install updates and new drivers.

Problem: But now I want to get back to BIOS, but I cannot!

• Pressing "Del" during boot will cause the display to stay black and the system would not boot at all, either to Windows or BIOS; the only way out is to Reset or Power down
• Doing nothing during boot will cause the system to boot to Windows, but I don't even see the MSI logo screen / system spec screen, nor the Windows logo scene; it just straight brings me to the Windows login screen

Attempted solution: I have the latest BIOS downloaded to a USB drive (FAT32) and can attempt to flash the system, but I would like to hear some thoughts from the forum before I proceed.

Question: What is going on with my machine and how do I get back to BIOS?

Solution 1:

Most foolproof, no-timing-required way:

Settings > Update > Recovery > Advanced Startup > Restart Now

In the blue-background screen that follows:

Troubleshoot > Advanced options > UEFI Firmware Settings

That will boot directly into the UEFI BIOS on your motherboard.

Solution 2:

Most likely not the optimal solution, but here's what I did:

1. Turned off PC
2. Removed the CMOS battery for a few minutes and put it back (shorting the Clear CMOS jumper did not work)

After this, I was back to the starting point of this journey: BIOS access, but no boot to Windows (boot mode was now UEFI). But I did get back to BIOS!

Next:

1. Flashed BIOS to latest firmware
2. Used a USB to clean-install Windows 10

Now the system is working as I expect it to: boot to Windows, access to BIOS if I want, and MSI + Windows logo screens.