Re-enabled CSM and Disabled Secure Boot and PC wouldn't post.

[+Tyranade Subscriber²]

So I decided to see what would happen if I had a UEFI install of Windows 8.1 and I re-enabled CSM and turned secure boot off and after saving the changes my PC restarted and then did not post until I popped out my Motherboard battery and reset everything.

 

So I was wondering why it did this and what I would need to do if I ever wanted to go back to a "Legacy" install of windows?

[+Tyranade Subscriber²]

So it might of been that even though I disabled Secure Boot I did not remove the Secure Boot Keys. I don't know I just did exactly what I did again and this time the system posted.

[+Warwagon MVC]

So it might of been that even though I disabled Secure Boot I did not remove the Secure Boot Keys. I don't know I just did exactly what I did again and this time the system posted.

 

ya what a pain the ass. I miss the old days of the Windows 7 motherboards.

[+Tyranade Subscriber²]

I just wanted to see what would happen if I turned it off. I don't know what wouldn't cause it to POST I changed the OS Type from Windows 8 back to other which is it default and I changed Boot Mode Selection to UEFI only with CSM on and my PC just didn't want to post as soon as I did that. 

 

I am assuming that UEFI is now the way forward and we won't ever be going back to BIOS again so I SHOULDN'T need to I just wanted to see how I would go back to BIOS if I ever needed to. Windows 7 and up can all be installed in UEFI mode so it isn't an issue.

 

Once I put the BIOS back to purely default settings it still booted off the UEFI install on my SSD until I changed the Boot Mode Selection to not include UEFI so it was only looking for old MBR installs.

 

Anywho I just wanted to know how to switch back. It seems that to enable UEFI and Secure boot you need to get the settings right of the computer has a fit.

[Boo Berry]

I always disable Secure Boot, Fast Boot and CSM on my motherboards once I get them.

[The_Decryptor Veteran]

Only way I can see enabling the CSM breaking things, is if it defaulted to the CSM to try booting the system. The CSM can't boot a UEFI install of Windows, so it probably thought you didn't have an OS. UEFI/CSM is a install time switch, you can't switch between after afterwards without reinstalling. CSM can't boot UEFI installs, and the UEFI can only boot a CSM install if it's enabled (Which it has no reason to be if all your hardware works under UEFI)

Also removing the Secure Boot keys is probably a bad thing, they don't lock the UEFI to a specific install, they just validate the install (People running Linux can sign their own kernel and insert the signing keys into the UEFI, etc.). Removing them and then enabling Secure Boot will probably just cause it to fail again (Unless the board is smart and re-adds them)

[+Tyranade Subscriber²]

What I couldn't figure out was why my computer decided not to post after I messed with those settings and I had to take out the motherboard battery to reset everything for it to POST again.

 

I has literally been fine since no issues what so ever, I am guessing I mushed up the settings when I turned the settings back to what they where (or what I thought they where) to see out of pure curiosity what would happen if I tried to boot a UEFI Install of Windows 8.1 with CSM on.

 

Also with UEFI booting and whatnot enabled why can I not see my 3 other HDDs in the boot list when I press F12 to select what drive to boot off of like I could before I turned the settings on to enable UEFI installs.

 

All my hardware works under UEFI. Z78 Motherboard, 4670K etc and Windows 7 all the way to 10 can all be installed in UEFI mode so I shouldn't need to touch them, I just wasn't sure why it would not even post after I played with the CSM etc settings.

[xendrome]

So I decided to see what would happen if I had a UEFI install of Windows 8.1 and I re-enabled CSM and turned secure boot off and after saving the changes my PC restarted and then did not post until I popped out my Motherboard battery and reset everything.

 

So I was wondering why it did this and what I would need to do if I ever wanted to go back to a "Legacy" install of windows?

 

So 1: You broke UEFI booting because Legacy looks for a partition table, and UEFI does not

And 2: You would need to reinstall Windows using a non-UEFI method

 

I'd personally stick to UEFI if your hardware supports it, faster boot times, resume, and device init.

[The_Decryptor Veteran]

I was running a UEFI board with the CSM enabled for a while (Thanks Nvidia), it worked fine because I had the UEFI bootloader first in the list, so it never relied on the CSM for booting anything. UEFI handles booting a hell of a lot differently to the CSM way, under UEFI the bootloader is "installed" into the UEFI, and it can actually see what OS you're running. The CSM method involves trying to read special sectors of drives and seeing if a bootloader was found. That's why the CSM lists every drive on the system as a boot device, while the UEFI doesn't, since it's smart enough to know you can't boot off them.

That does give one problem, if you have a UEFI install and the CSM enabled, but the boot order wrong, the CSM will see your main hard drive as bootable, but be unable to load the bootloader (Since it's in a different format), and try falling back to something else (And depending on how it's setup, it might not try UEFI booting at all, I know my board was originally configured like that)

[sinetheo]

So it might of been that even though I disabled Secure Boot I did not remove the Secure Boot Keys. I don't know I just did exactly what I did again and this time the system posted.

 

Odd

 

I have disabled secure boot on 8.1 before and it still booted fine. That is not the cause. Is it BSOD or will it not even PST?

[+Tyranade Subscriber²]

So yeah I am guessing I broke my system because it decided to have a fit and tried to boot using CSM while I had it set up for UEFI which caused it not to post. Lesson learned do not mess with that unless I want to go back to an old style install. 

 

Thanks for the help. UEFI booting is pretty new to me as I only just realized it was a thing hence why I Swapped my install over to it.

 

Oh and a question I am dual booting Windows 8.1 and 10 and when I hit F12 to pick which drive to boot from it only shows my SSD still, this is because all the boot files and all that is on the SSD and not on the HDD with windows 10 as well right?

[The_Decryptor Veteran]

Yeah, Windows uses a single bootloader for everything (Similar to Grub under Linux), so even if you're dual booting 8 and 10, you'll only have one entry in the UEFI boot selection (Under the CSM you'll have the option for both drives, even though only one will boot, etc.)

[Radium]

In UEFI, you put EFI files on the EFI System Partition and create pointers to them in a piece of flash memory on the board. You don't boot the drive, you load a specific file. The first sector on a properly set up drive with GPT has a protective MBR that's not flagged as bootable.

 

Edit:

HINT!

Linux no longer needs middleware boot loaders on UEFI systems. Compile the kernel with an EFI stub and UEFI can load it directly. Use efibootmgr (dependency: lspci & efivars) to put it into the boot list.