Can’t enable “Launch CSM” option on ASUS mobo

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I’m hoping some BIOS guru will be able to help me with this problem. I’ve built numerous desktop computers over the years, both for myself and others, so I’ve been fairly comfortable at entering the BIOS and dealing with making changes as needed. Whenever I’ve built a new computer, rarely do I have to do this, and by no means do I consider myself an expert at this. The results I’ve gotten are computers that, of course, boot normally off their C: drives, but could boot from a USB or DVD disc when needed. A recent attempt at booting from one of these drives (to run Spinrite) brought me to this question. I find I can not get my current computer to boot from either the USB or the DVD, no matter what I try.
It seems to me, from the research I’ve done, that the problem lies with CSM and Secure Boot. The computer in question has an Asus Prime B760-Plus mobo. I have another test computer I can use for comparison that has an older Asus Prime B250M-A mobo. On that computer, I can go into the BIOS, go to the boot settings screen, and set the “Launch CSM” setting to Enabled. It also indicates that “Boot device control” is set to “Legacy and EUFI OPROM.” When I inspect the Secure Boot setting, it shows that Secure Boot is enabled. The result is, when I bring up the boot menu on that computer, it shows a “non-EUFI” option for my flash drive if it’s inserted. I can then boot from that.
BUT, on the computer in question, the same option in the BIOS screen to enable “Launch CSM” is greyed out, and therefore cannot be changed. I have tried just about every setting change I dare to make, and nothing has worked to allow CSM to be enabled. So, I can’t boot this computer from a USB or a DVD. Not only can’t I run a utility like Spinrite, if I needed to do a clean bare-metal install from my original Windows 11 disc, I won’t be able to do that.
I’ve even resorted to clearing the CMOS header by shorting 2 pins on the mobo, to updating the BIOS, but neither process has made any difference.
So, if anyone can shed some light on my issue, I’d greatly appreciate it. TIA

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abrayshaw wrote:

I have tried just about every setting change I dare to make

Have you tried setting BIOS to default ?

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Yes, I tried setting the BIOS to default settings. It made no difference.

Thanks

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Alex5723

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1. On some ASUS motherboards, having Secure Boot enabled forces CSM/UEFI mod with no option to change it.

Try disabling Secure Boot?

2. The integrated graphics card in some of the Intel’s newer CPUs don’t support VBIOS which forces CSM/UEFI mod with no option to change it.

Either use a 3rd party graphics card with VBIOS support or swap the CPU for one with VBIOS integrated graphics?

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abrayshaw wrote:

BUT, on the computer in question, the same option in the BIOS screen to enable “Launch CSM” is greyed out, and therefore cannot be changed. I have tried just about every setting change I dare to make, and nothing has worked to allow CSM to be enabled.

If I understand you correctly, you are trying to set CSM (Compatibility Support Module) to “ON”. I agree with you, that is very strange that you can not enable it. I have a new Asus Prime Z790-V AX which is probably using the same UEFI BIOS, and I have no problem setting it to ON for compatibility mode or OFF  for Windows UEFI only. Just for a data point.

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abrayshaw wrote:

It seems to me, from the research I’ve done, that the problem lies with CSM and Secure Boot.

CSM is intended to boot in Legacy Mode / MBR.

Is this a MBR SSD ? If so convert to GPT.

https://www.partitionwizard.com/partitionmanager/csm-support-bios.html

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@Alex5723, if you actually read the all the way thru the opening post you’d see the poster indicated…

abrayshaw wrote:

I can’t boot this computer from a USB or a DVD.

So your suggestion to covert to GPT is completely useless!

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Alex5723

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Disk is already a GPT. Since my last post, I determined that Window’s System Information shows me that Secure Boot State is Off. Now I’m really confused!

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I just wanted to add, that with CSM Off, (UEFI mode only), you can format your USB to boot with UEFI. This is a copy of my boot selection screen. C: Drive and two backup recovery boot disks on one of my USB drives.

 

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