Disabling CSM doesn't allow boot to Windows

Supra said:

So I can't use this without buying it; converting to FAT32 is a 'Pro' feature that even the Demo won't allow me to do. Would EaseUS or AOMEI do the job?

The other programs might be able to.

NavyLCDR said:

The other programs might be able to.

I'm unable to convert, but so far with MiniTool I've created a new FAT32 partition (is 350MB too much?), but I can't set it as active, even if I set the current System Reserved as inactive and apply. Can't set actives in Disk Management, only MiniTool.

Supra said:

I'm unable to convert, but so far with MiniTool I've created a new FAT32 partition (is 350MB too much?), but I can't set it as active, even if I set the current System Reserved as inactive and apply. Can't set actives in Disk Management, only MiniTool.

You created it as a logical drive. Logical drives cannot be set as active, only primary partitions can. Once you get it created as a primary partition, assuming that it retains drive letter F: after it is set as active, the bcdboot boot command will be:

bcdboot C:\Windows /s F: /f ALL

NavyLCDR said:

You created it as a logical drive.

Copy that, knew logical had something to do with it but wasn't sure what to do.

It's been set as primary, active, and entered the command again just to be sure. Should I reboot? I am scared.
Does this look right?

what are the files/folders on F: drive? Do you have a bootable rescue USB thumb drive created? If it fails, you would need to boot from the rescue USB flash drive, get to a command prompt, run diskpart:

diskpart
list disk
select disk # <-replace # with the actual drive the computer should boot from
list part
select part # <-replace # with the actual partition number of the OLD system partition
active
exit
exit

Then you should be back to booting again if the new system partition should not boot. But, as long as the bcdboot command completed successfully, you should be good to go to boot in UEFI mode.

Now you can use MiniTool Partition Wizard to clean up your drive a bit. Remove the extra system partition in front, maybe shrink down the new system partition at the end to 150 MB or so, expand your C: drive to fill the empty space created.

If you want to.

NavyLCDR said:

I like to use MiniTool Partition Wizard Free:
Best Free Partition Manager for Windows | MiniTool Partition Wizard Free

Normally Windows won't let you mess with the system partition the computer boots from, but MiniTool Partition Wizard will. You can attempt to just convert the NTFS system partition to FAT32 with it. Then assign a drive letter to it, let's say T:. Then the bcdboot command would be:
bcdboot C:\Windows /s T: /f ALL

That would make it bootable in both CSM and UEFI modes. Or you might have to delete the partition, create a new FAT32 partition, mark it as active, then use the bcdboot command. I would highly recommend having an image backup before you mess with the system partition if you don't know how to create it from scratch using a bootable USB rescue flash drive.

The requirements for booting basically are:
Legacy BIOS or CSM mode:
MBR drive
FAT32 or NTFS primary partition marked as active (can be the Windows partition)
BIOS compatible BCD

UEFI:
MBR or GPT drive
FAT32 partition (therefore must be separate from the Windows partition)
UEFI compatible BCD

Therefore, an MBR drive with a FAT32 primary marked as active with a BCD containing files compatible with both BIOS and UEFI booting will boot in either mode.

It's been over a year since the last thread but I needed to thank NavyLCDR for his contribution. I was in the same situation as Supra, an SSD with Windows 10 (2004 version) in a system that got upgraded and I didn't want to format it or change it to GPT (because no actual advantage) but yet needed to boot in UEFI mode.

NavyLCDR was right about the BCD but I must warn other users about the Minitool Partition Wizard. I purchased this software and eventually it cannot convert the (Boot) System Partition (200MB or so) from NTFS to FAT32, it gives a message that it's a system partition and it fail to boot etc. I found a workaround that can be done with other partition management software too (maybe even windows?!!?). The steps are the following:

1) I resized (shrink just a bit) the main C: partition in order to get some unallocated space.
2) Then, I copied the System Partition (using Partition Wizard), creating an identical one on the same disk
3) I converted this new partition to Fat32 (it was NTFS just like the original)
4) The new partition was automatically given a letter(L) after the copy, I ran “bcdboot C:\Windows /s L: /f ALL” (to update the BCD) from CMD (admin rights required) and then I got rid of the letter (L) on the new partition.
5) I made the new partition active
6) System restart and boot into bios to disable the CSM (enable UEFI mode)
7) Done. Boot into windows in UEFI mode, no problems at all.

The original system partition can be deleted to free up space or just left as it is, afterall it's only 200MB. I cannot stress this enough, have an image backup before attempting this procedure! You never know what might go wrong. In addition, I read in other online sources that Windows does not like booting UEFI from MBR disks and that may lead to major problems with updates not working etc. That may be true but I don't have any such problems what so ever.

That's it. Have a nice day.