MSI B850M Mortar Wifi - bios A49 - errors during windows 11 installation

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sojer2005

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I had to reinstall Windows 11, and unfortunately, I think there is a problem with the new BIOS that I installed yesterday (version A49). To my surprise, after copying the installation files and restarting (initial installation stage), the installer displays this message. I manage to move-force the installation forward by simply performing a hard reset, but after installing Windows, it reappears. What is going on?
For the record I have done many win 11 reinstalls on UEFI A45 - same hardware - never have such problems before.

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A few questions just clarity. Did you update the BIOS to A49 before doing a clean installation of Windows? Did you remove all partitions on the SSD before formatting the SSD as part of the installation process?

With Inaccessible boot device I think of two things in first instance. First thing would be running UEFI mode with SSD formatted with MBR or running CSM mode with SSD formatted with GPT. That doesn't make sense because with the installation Windows would have formatted the SSD in accordance with the setting from the BIOS (UEFI or CSM mode). So that hypothesis goes out of the window.

The second question would be about the health of the SSD. Can you post a screenshot of the health of your SSD with CrystaldiskInfo tool?

A third question would be what happens when you go back to A45? Does it fix the issue with the freshly installed Windows? If it runs stable after having checked the integrity of Windows installation and file system then I would be interested to see what happens when you would update the BIOS to A49. But that is far ahead for where things stand now.
 
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ok. New BIOS (A49) installed, all factory settings restored - clear CMOS, two NVMe drives: WD WD SN7100 (M2 slot) and Crucial P3 Plus (M1 slot) - completely new, PC assembled in September 2025, in perfect condition - no errors.
It was supposed to be a clean installation of Windows 11 on freshly formatted drives (via Gparted Live USB)
Before installation, the drives were formatted, GPT. BIOS in UEFI mode. All settings at default.
Going back to A45 solves the problem completely.

Someone posted this o reddit also LINK

Windows eventually installs by forcing to reboot via hard reset (power off), but sometimes when it starts up, a message appears saying “inaccessible boot device” (ver A49).

To be frank, I saw this behavior in previous beta versions that were withdrawn (a47, a48 I think). I didn't report it here, but I see that A49 appeared on the official website and the problem remained—either it hasn't been noticed/investigated by anyone yet.
 
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sojer2005 said:
Going back to A45 solves the problem completely.
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That's a clear indication. Thank you for reporting this
sojer2005 said:
Someone posted this o reddit also LINK

Windows eventually installs by forcing to reboot via hard reset (power off), but sometimes when it starts up, a message appears saying “inaccessible boot device” (ver A49).
Click to expand...
Corroborating evidence. :cool:
sojer2005 said:
To be frank, I saw this behavior in previous beta versions that were withdrawn (a47, a48 I think). I didn't report it here, but I see that A49 appeared on the official website and the problem remained—either it hasn't been noticed/investigated by anyone yet.
Click to expand...
With recent motherboards MSI changed the naming convention. With 'older motherboards' it would release betas with the beta designation. With more recent boards stable releases also known as roduction releases, the one that get flashed on new motherboard, end at 0. The releases ending at numbers other than 0 like A47, A48 and A49 are betas in disguise. :undecided:

I cannot tell whether this problem has been reported to MSI or not. So, please consider it reporting to MSI through the official channels making sure to also point to the Reddit topic you found.

The A49 release is based on (what appears to be) a pre-release of AMD's Agesa 1.3.0.0. In that sense it very new.

I am happy going back to A45 brings you back to stability.
 
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Further details for those interested. I decided to give the A49 a second shot and reinstalled that BIOS version. As I mentioned, I have two M.2 drives – a Crucial P3 2TB Plus and a SanDisk SN7100 2TB – both of which appear to be on MSI's list of approved drives for my motherboard. Previously, my configuration was such that Win 11 was on the Crucial and Linux was on the WD. The A49 BIOS in this configuration gave me a hard time, Win was difficult to install - a series of errors about “device boot inaccessible” (everything was OK on the A45).

But this time I swapped the operating systems: I installed Win11 on WD and Linux on Crucial. And everything went back to normal. Win11 installed without errors on the first try and starts up normally every time. Linux on Crucial reports no errors. So I have no idea what could have caused this? Any ideas?
 
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Just a total long shot. When installing Windows 11 did you make sure all partitions on it were deleted? Windows will, with a clean install, install multiple little extra partitions: EFI, System Reserved and Recovery Partition. They all need to be removed before clean installing Windows 11. When one or more are still present the installation may bork.
 
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ericj159802e9 said:
Just a total long shot. When installing Windows 11 did you make sure all partitions on it were deleted? Windows will, with a clean install, install multiple little extra partitions: EFI, System Reserved and Recovery Partition. They all need to be removed before clean installing Windows 11. When one or more are still present the installation may bork.
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Yes, I have nuked everything very thoroughly :)
 
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Have you checked if there's any firmware update for WD SN7100?
Do you mean error appears when WD SN7100 has Linux on it and it is installed in M2_2, and you tried to re-install Windows 11 on Crucial P3 PLUS (M2_1)?
 
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fatedust said:
Have you checked if there's any firmware update for WD SN7100?
Do you mean error appears when WD SN7100 has Linux on it and it is installed in M2_2, and you tried to re-install Windows 11 on Crucial P3 PLUS (M2_1)?
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Hi, both drives have the latest firmware. These numerous “boot device inaccessible” errors only appear when Win11 is installed on Crucial P3 Plus and only on the A49 BIOS version. After reinstalling Win11 on the WD drive (still on BIOS A49), the errors stopped.

There were no errors on version A45.
Linux works fine on all drives, regardless of the BIOS version.
I did not physically swap the drives, only the operating systems installed on them.
 
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Okay. Good news. I installed yesterday's new version (7E61v1A4A) and took the trouble to reinstall Win 11 on Crucial P3 Plus, and this time everything works great. So any bugs from previous BIOS versions have been fixed. Good job and thank you.
Oh, and one small observation: the “Fast boot” option has completely disappeared from the Win11 settings. I remember that it was definitely available before, because I always turn it off. This time, after going to the Control Panel, it is nowhere to be found.
 
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dvair said:
If you disable hibernation, the Fast Boot option disappears.
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Hi, I didn't disable any functions myself—there are no hibernation or fast boot options in the control panel right after a clean installation of Windows 11.
On versions earlier than 7E61v1A4A, both functions were available (i.e., definitely "fast boot" because I always turn it off immediately after installation).
edit:
Strange, it's still visible in the registry...
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sojer2005 said:
Hi, I didn't disable any functions myself—there are no hibernation or fast boot options in the control panel right after a clean installation of Windows 11.
On versions earlier than 7E61v1A4A, both functions were available (i.e., definitely "fast boot" because I always turn it off immediately after installation).
edit:
Strange, it's still visible in the registry...
Click to expand...
OK, the "fast boot" and "hibernation" options appeared out of nowhere. It must be some kind of Windows 11 quirky behavior.
 
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sojer2005 said:
OK, the "fast boot" and "hibernation" options appeared out of nowhere. It must be some kind of Windows 11 quirky behavior.
Click to expand...

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1768710219110.png
 
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artur.aragao@outlook.com.br said:
Dear,

I looked at your post and noticed that it has been updated to the version shown in the image.

www.msi.com

MAG B850M MORTAR WIFI | Gaming Motherboards｜Best Motherboard for AI PC｜MSI

MAG B850M MORTAR WIFI AMD AM5 gaming motherboard offers advanced connectivity with Wi-Fi 7, 5G LAN, high-speed USB, DDR5, PCIe 5.0, and M.2 Gen5. Designed for AI PCs and EZ DIY, this is the best B850 MATX motherboard for AMD Ryzen 9000 processors.
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View attachment 208988
Click to expand...
Thanks. These settings have returned to their normal state; I don't know what caused the issue.
 
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