Windows installed without a USB installer connected to my system

PhilB · Jun 10, 2026

A system for which I had to do an emergency recovery and had a completely empty NVM drive started to install windows after I resolved the BIOS issues. But there was no USB Windows installer connected to the system. I'm wondering how all this was actually possible. How did the windows installer know which version of Windows to install? Before I started this install process I disconnected both Ethernet cable and WiFi antenna. so, I could set up windows with a local admin account rather than a Microsoft account.

When I first started this process, I erased all existing partitions on the NVMe drive. I had some issues with the existing BIOS which is downrev from the current version. That BIOS had bugs in the selection of boot drive options, for example windows manager or USB UEFI drive... I struggled and struggled and struggled but I was never able to boot the system into the windows installer USB.

I had to do an emergency recovery because a BIOS flash was corrupted. Google search helped me to do the recovery and was actually more helpful than the motherboard manufacturer tech support.(MSI X870E Carbon WiFi)

After I was able to do a successful BIOS install (thank you Google) I expected my system to boot into BIOS, because I did not have a USB Windows installer present.at that time. Instead, it booted into windows install or. However, it skipped some of the preliminary steps like the version of Windows I wanted to install, pro versus home had my license. When windows was fully installed, I had a pro version installed, just as I had with my previous Windows install.

JLArranz · Jun 10, 2026

Supposing you haven't got one of those very small sized pendrives connected, or a disc left in a DVD... I've read several times from MS that the Windows Recovery disk can reinstall what you had in Windows or something along those lines. Doing one here in my semi-powerful W10 (FX8350) or basic performance W11 (10 watts Celeron J4125) takes several hours and I've always supposed they're spent in compiling what is installed.

It sounds to what prebuilts do when first connected... The wifi antenna isn't a digital requirement, but an analog help, it's possible that the connection works w/o it.

I'd look for apps and things you had installed but aren't installed in a clean Windows install. Maybe something was able to unformat the drive. It's physically possible, but it must be programmed somewhere and Idk if such thing exists in BIOSes or in an ad hoc cloud service. I'd also suspect it could have been an "automatic repair install", totally ignorant if such things are done or in what circumstances.

Celery · Jun 10, 2026

x509 said:
Before I started this install process I disconnected both Ethernet cable and WiFi antenna. so, I could set up windows with a local admin account rather than a Microsoft account.

You don't need to disconnect from the internet to set up a local account. Just run:

start ms-cxh:localonly

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x509 said:
I had some issues with the existing BIOS which is downrev from the current version. That BIOS had bugs in the selection of boot drive options, for example windows manager or USB UEFI drive... I struggled and struggled and struggled but I was never able to boot the system into the windows installer USB.

One thing to try would have been resetting the BIOS to its default settings, which restores the default boot configuration (see image below).

When a Windows 11 installation USB flash drive is connected and the system is started using the one-time boot menu key (F11 on MSI motherboards), the USB device should appear in the boot menu if it was created correctly and detected by the firmware. This allows the system to boot from the installation media without changing the permanent boot order in the BIOS.

MSI motherboard boot order priorities - 1.webp

Here is the breakdown of how MSI motherboards handle boot order priorities.

1. FIXED BOOT ORDER Priorities

This is your Master List. It defines the order of device types.
In this menu, you aren't usually selecting a specific brand of hardware (like "Samsung 990 Pro"). Instead, you are telling the motherboard which generic category to try first.

Common Options: UEFI Hard Disk, UEFI USB Key, UEFI CD/DVD, UEFI Network.
The Logic: If "UEFI Hard Disk" is set to Boot Option #1, the motherboard will look for a storage drive to boot from. If you have three different hard drives plugged in, it then looks at the BBS Priorities to decide which of those three to use.

2. UEFI Hard Disk Drive BBS Priorities

This is your Sub-Selection List. "BBS" stands for BIOS Boot Specification.
This menu only becomes relevant if you have multiple devices of the same type (e.g. two different M.2 NVMe SSDs or several USB sticks).

The Logic: This setting determines the internal ranking within the "Hard Disk" category.
The Example: If two Windows Boot Manager entries exist (i.e. two Windows installations, each using its own EFI system partition), this menu can influence which entry appears first in the F11 boot menu.

Windows Setup automatically creates a UEFI boot entry in NVRAM (Non-Volatile Random-Access Memory) that points to \EFI\Microsoft\Boot\bootmgfw.efi on the EFI system partition. On most UEFI/GPT systems with a single Windows installation, manual boot-order changes are usually unnecessary because the firmware automatically boots the Windows Boot Manager entry stored in NVRAM (see image above).

Try3 · Jun 10, 2026

x509 said:
a completely empty NVM drive

What was shown in Disk mgmt?

Denis

PhilB · Jun 10, 2026

Try3 said:
What was shown in Disk mgmt?

Denis

To reply to several post above, I need to point out that my system was bricked, according to MSI support, needing a warranty RMA to fix. Fortunately Google knew better. The key point is that once there was a successful BIOS install, the system started to install Windows without any intervention or action by me. Maybe I didn't explain that clearly enough in my OP.

PhilB · Jun 10, 2026

JLArranz said:
Supposing you haven't got one of those very small sized pendrives connected, or a disc left in a DVD..

No. Just a pendrive with a good BIOS file named MSI.ROM, and only that file. Nothing else.

JLArranz said:
It sounds to what prebuilts do when first connected... The wifi antenna isn't a digital requirement, but an analog help, it's possible that the connection works w/o it.

I didn't know that. But at one point, the installer said that i wasn't connected to the Internet.

JLArranz said:
I'd look for apps and things you had installed but aren't installed in a clean Windows install. Maybe something was able to unformat the drive. It's physically possible, but it must be programmed somewhere and Idk if such thing exists in BIOSes or in an ad hoc cloud service. I'd also suspect it could have been an "automatic repair install", totally ignorant if such things are done or in what circumstances.

If we think of Occam's Razor, how would such a program be included in an installer created with Media Creation Tool.

Wannagofast · Jun 10, 2026

PhilB said:
When I first started this process, I erased all existing partitions on the NVMe drive. I had some issues with the existing BIOS which is downrev from the current version. That BIOS had bugs in the selection of boot drive options, for example windows manager or USB UEFI drive... I struggled and struggled and struggled but I was never able to boot the system into the windows installer USB.

I'm just gonna assume a few things here, take a wild stab at an explanation, and hope I'm right in my thoughts...

So it sounds like you were able to boot from the USB at first and made it to the point that you delete all partitions and select where to install Windows. Right after that the installer will create the necessary partitions, and copy the windows installer to your drive. Then it reboots the computer. Upon rebooting is when you had "bios issues" (possibly related to secure boot) I have seen this recently with my MSI motherboard and a blank drive. So it would make sense that once you got the "bios issues" sorted out that it would continue to go about finishing the Windows install that you started. It wouldn't need a usb anymore because the installer was already copied to the drive.

If that's not what happened then you can just ignore this and chalk it up to an old mans ramblings.

peace
wanna

PhilB · Jun 10, 2026

Wannagofast said:
I'm just gonna assume a few things here, take a wild stab at an explanation, and hope I'm right in my thoughts...

So it sounds like you were able to boot from the USB at first and made it to the point that you delete all partitions and select where to install Windows. Right after that the installer will create the necessary partitions, and copy the windows installer to your drive. Then it reboots the computer. Upon rebooting is when you had "bios issues" (possibly related to secure boot) I have seen this recently with my MSI motherboard and a blank drive. So it would make sense that once you got the "bios issues" sorted out that it would continue to go about finishing the Windows install that you started. It wouldn't need a usb anymore because the installer was already copied to the drive.

If that's not what happened then you can just ignore this and chalk it up to an old mans ramblings.

peace
wanna

@Wannagofast Actually that sounds plausible, sort of. However, I am still bothered the fact that when I was struggling with the old BIOS, I never could get past a reboot that started with the USB installer. And I doubt that I could reproduce this situation. However, it is the best explanation I have.

Try3 · Jun 11, 2026

PhilB said:
The key point is that once there was a successful BIOS install

I would suggest that there is a manufacturer's 'factory restore' partition and that once you had fixed the Bios, that was what found & installed from i.e. in the absence of any installed OS, the Bios handed over to that when the Bios had loaded.
Disk mgmt should confirm that possibility or eliminate it.

Denis

PhilB · Jun 11, 2026

Try3 said:
I would suggest that there is a manufacturer's 'factory restore' partition and that once you had fixed the Bios, that was what found & installed from i.e. in the absence of any installed OS, the Bios handed over to that when the Bios had loaded.
Disk mgmt should confirm that possibility or eliminate it.

Denis

Since Windows is already installed, how would I is disk management to confirm or eliminate that possibility?

Try3 · Jun 12, 2026

PhilB said:
how would I is disk management to confirm or eliminate that possibility?

By showing the partitions including any manufacturer's 'factory restore' partition [which is typically about 14GB].

Windows must have come from somewhere.

Denis

Megahertz · Jun 12, 2026

You must have a Win 11 installation somewhere in your drive.
I agree with Denis. It was probably a factory recover that install Win 11. And it probably installed an old version of Win 11.
Please post a whole window Disk Manager image of ALL your drives. Don't forget to expand the columns so we can read them. How to Post a Screenshot of Disk Management
If you have a MiniTool or AOMEI Partition use it instead or Windows disk manager.

Wannagofast · Jun 12, 2026

Based on the assumption that the OP is referring to the computer listed in his bio a factory restore partition seems highly unlikely. There are not normally factory restore partitions on a home built DIY computer.

Peace
Wanna

PhilB · Jun 13, 2026

Megahertz said:
You must have a Win 11 installation somewhere in your drive.
I agree with Denis. It was probably a factory recover that install Win 11. And it probably installed an old version of Win 11.
Please post a whole window Disk Manager image of ALL your drives. Don't forget to expand the columns so we can read them. How to Post a Screenshot of Disk Management
If you have a MiniTool or AOMEI Partition use it instead or Windows disk manager.

In response.

spapakons · Jun 13, 2026

The only explanation I can think of, given that you deleted all partitions on NVMe disk so there was no Recovery partition, that the Windows setup files were saved in some dedicated ROM in BIOS. The BIOS detected the disk was empty and started installing Windows from the ROM.

garlin · Jun 13, 2026

spapakons said:
The only explanation I can think of, given that you deleted all partitions on NVMe disk so there was no Recovery partition, that the Windows setup files were saved in some dedicated ROM in BIOS. The BIOS detected the disk was empty and started installing Windows from the ROM.

Windows install images have been larger than 1-2 GB for over two decades. No OEM is dedicating that much ROM or flash memory to hold something you might hardly use. Plus the chips would have to take up board space.

Megahertz · Jun 13, 2026

Wannagofast said:
Based on the assumption that the OP is referring to the computer listed in his bio a factory restore partition seems highly unlikely. There are not normally factory restore partitions on a home built DIY computer.

Peace
Wanna

I agree.
To install Win 11 you must be running a OS (Windows, Win PE, Win RE)
- It wasn't from a Factory recovery partition.
- It wasn't from the internet
- It wasn't from a USB drive
So the question is: Where did the installation files came from?

spapakons · Jun 13, 2026

Unless he deleted all the partitions without deleting the recovery partition because Disk Management inside Windows prevents this so as not to accidentally make the system unrecoverable in case of failure.

garlin · Jun 13, 2026

If this PC has a MSI motherboard, there won't be an OEM recovery partition and to my knowledge, MSI doesn't provide a vendor tool to create a recovery USB image or make a factory recovery partition for you.

@Wannagofast's theory makes the most sense. At some point, a Windows install or recovery USB drive started the install or recovery process. Typically this involves extracting an install image to a mounted filesystem. When finished, Setup runs bcdboot to prepare the BIOS to boot into the freshly extracted Windows to continue the rest of the install.

Assuming there was a corrupted BCD store or bad BIOS settings, then it can't find the boot manager. After clearing up the problem, BIOS detects there's a valid EFI volume with a working boot manager. So it boots into the unfinished Windows and continues processing.

The question would have been AT THE TIME, what version of Windows was installed? Not what version it may have ended up, because Windows Update would have patched the system. If you knew the exact Windows version it would rule out different possibilities as to where it came from.

A too recent initial Windows build would rule out something left over from when the PC was purchased.
A too old initial Windows build would rule a recent recovery image that was built.

PhilB · Jun 13, 2026

spapakons said:
Unless he deleted all the partitions without deleting the recovery partition because Disk Management inside Windows prevents this so as not to accidentally make the system unrecoverable in case of failure.

Possibly. I don't remember the method that I used to clear out all the partitions, except that the NVMe drive was reported empty.

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