Are you stuck with the error ‘An Operating System Wasn’t Found’ when booting Windows? We can help you with it.

Here at Bobcares, we have seen several such Windows-related errors as part of our Server Management Services for web hosts and online service providers.

Today we’ll take a look at the causes for this error and see the fix.

Why does ‘An Operating System Wasn’t Found’ error occurs when booting Windows

Generally, this error occurs if there is no operating system bootloader found on the current disk. So, the computer can’t find and start the Windows bootloader.

As a result, it will throw the below error message.

Here are some reasons for this error to occur

• The system partition is damaged, missing, or damaged MBR (master boot record).
• No active partition or an incorrect disk partition is marked as active
• Boot configuration data (BCD) is corrupted
• The HDD that has an OS installed it not connected.

How to fix the error ‘An Operating System Wasn’t Found’ when booting Windows

Now let’s take a look at the steps our Support Engineers provide to resolve this error.

Before moving to the solution part, make sure the following points.

1. The hard drive and the OS must be connected.
2. You have connected the power and ribbon cables properly.
3. Generally, the hard drive is detected in the BIOS/UEFI of the computer. Make it the primary boot device;
4. Finally, check the Secure Boot settings in UEFI. They may have been changed (check if Windows is booted with the Secure Boot mode enabled/disabled and in the Legacy mode).

After checking the above details, if the Windows still doesn’t boot then restore the Windows bootloader and disk boot record.

Identify Disk Partition Table & Windows Partition

First, you need a Windows to install media (on a CD/DVD/ bootable USB drive) or rescue disk with the same OS version you have installed on your drive.

Now change the boot order in BIOS(UEFI). For that, boot from your installation/rescue disk and run the command prompt.

You must need to detect the type of the partition table on the disk whether it is GPT or MBR. Because the method for restoring the Windows bootloader depends on it.

So run the below command.

diskpart

Then enter the below command.

list disk

As the result of the above command, if there is an asterisk(*) in the Gpt column then the GPT partition table is used, otherwise it is MBR.

Display the list of volumes on the disk. For that, run the below command.

list vol

Exit the diskpart session by entering the below command.

exit

By looking at the disk size, Windows is likely to be installed on E: drive. So, confirm it by running this command.

dir e:

If Windows is present then you must see Windows, Program Files, Users, and other standard folders on the drive.

Finally, now we have found the disk layout type and the drive letter of the disk Windows is installed on.

How to Repair the Windows Bootloader on the MBR Disk?

Here we are considering that the computer is using BIOS and the disk partition table is MBR.

First, create bootloader configuration files on the E:\ drive:

bcdboot E:\Windows /S E:

As a result, the “Boot files successfully created” message will appear.

Next, re-create a Master Boot Record (MBR):

bootrec.exe /FixMbr
bootrec.exe /FixBoot
bootrec.exe /RebuildBcd

Now, make the Windows partition active by running the below commands.

diskpart
list disk
sel disk 0
list vol
select volume 2 (earlier we detected that Windows is installed on this volume)
active
exit

Finally, restart the computer and ensure that Windows has booted correctly and the “Operating system not found” error has not appeared.

How to Repair the EFI Bootloader on a GPT Disk of UEFI Computer

In case, if your disk has the GPT partition layout, then your computer must be using the UEFI architecture instead of BIOS.

First, find a FAT32 hidden partition and assign a drive letter to it (the size of this partition is 100-300MB, it is used to store the Windows bootloader which is called the EFI bootloader).

Diskpart
List vol

Consider that you’ve detected it as volume 1 with the label BOOTSTRAP.

Now select this EFI partition and assign a drive letter to it:

select volume 2
assign letter M:
exit

Then re-create the BCD bootloader configuration file:

cd /d m:\efi\microsoft\boot\
ren BCD BCD.bak
bcdboot E:\Windows /l en-us /s M: /f ALL

Finally, reboot the computer. Then remove the boot media (USB flash drive) and make sure that Windows has booted correctly.

[Need any further assistance in fixing Windows errors? – We are here to help you]

Conclusion

In short, this error occurs if there is no operating system bootloader found on the current disk. Today, we saw the solution provided by our Support Engineers.