> Windows can't boot after deleting system partition

Delete System Reserved and EFI Partition Windows Can't Boot – Fixed

Don't Delete System Partition, or Windows Will Be Unbootable

You would feel helpless and desperate when Windows can't boot due to mistakenly deleting system partition, like the following man:

Since there are many strange partitions on my laptop hard drive, including one EFI system partition, two recovery partitions, one OEM partition, and one small partition not having name, I deleted the 100MB EFI system partition as well as the small partition with third party tool and hope to add released space to drive C. Then, nightmare comes. My Windows 8 totally crashed and become unbootable. Someone told me it is because of deleting the EFI system partition. What should I do now? I don't want to reinstall, because lots of important files are stored.


Actually, there are lots of other folks facing similar issues, apart from you and the man in the example above.

So in today's post we will show why Windows won't start after system partition is lost as well as how to make Windows bootable again.

Why Windows Can't Boot after Deleting System Partition

As long as knowing what is system partition or what role the partition plays during booting Windows, you will get the answer.

Tip: since there are 2 types of booting mode, namely Legacy BIOS + MBR and UEFI + GPT, we talk about this issue from 2 aspects.


What Is System Reserved Partition ( Legacy BIOS + MBR)


When you are installing Windows 7/8/8.1/10 on a clean disk which is initialized to MBR, the setup will create a system reserved partition at the beginning of the hard disk and mark it active. It does not have a letter, so you can't find it in Windows Explorer or Computer but only visible in Windows Disk Management or other special tools. This partition holds the Boot Configuration Database (BCD), Boot Manager (BOOTMGR), and Windows Recovery Environment and reserves space for the startup files which may be required by BitLocker, among which BCD and BOOTMGR are vital parts to start Windows.

Then, let's see how Windows is loaded and running.

After we power on the computer, BIOS will perform Power-On-Self-Test (POST). When the test is completed, BIOS will look for and pass boot control to MBR (Master Boot Record). Then, MBR reads master partition table to find the active partition, namely the system reserved partition, and reads partition boot record of the system partition to locate and give boot control to Boot Manager. Boot manager then reads BCD which contains the menu entries that are presented by the BOOTMGR, and these entries can be: Options to boot Windows by invoking winload.exe, Options to resume Windows from hibernation by invoking winresume.exe, etc. If there are multiple Windows OS, we are able to choose which Windows to boot. After a Windows OS is selected, BOOTMGR will invoke winload.exe to load the corresponding Windows kernel as well as the core device drivers so as to boot Windows. 

You might feel a little bit diffult to get an understanding of the description above, so below we give a flow chart showing how Windows is loaded.

computer boot process on legacy bios

If the active system reserved partition is lost, Windows will be unbootable since no BOOTMGR and BCD are found. And you may receive error messages, like BOOTMGR is missing or Operating System not found.

What Is EFI System Partition (UEFI + GPT)


When you install Windows on a clean disk that is initialized to GPT, Setup will create an EFI partition (aka ESP). It contains the boot loaders or kernel images for all installed operating systems which are contained in other partitions on the same or any other local storage device, device driver files for hardware devices present in a computer and used by the firmware at boot time, system utility programs that are intended to be run before an operating system is booted, and data files such as error logs.

When a computer is powered on and booted, UEFI firmware loads files stored on the EFI system partition to start installed operating systems and various utilities. If the EFI system partition is lost, Windows will be naturally unbootable due to missing boot files.

Therefore, once system partition (either system reserved partition or EFI system partition) gets lost, Windows can't boot.

"Now tell your friends why deleting system partition will make Windows unbootable"

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But luckily, you still have a chance to make the unbootable Windows bootable again, and no reinstallation is required or at least reinstall without losing personal data. That is to recover the mistakenly deleted/lost system partition or fix boot information.

Further reading: deleting a partition in Windows just clears or modifies corresponding partition information in partition table, making Windows unable to locate the partition, and the actual partition still reside in its place until new partition is created there. Therefore, as long as we rebuild partition table, the lost partition would be visible for both Windows and users.


Then, let's see how to do the recovery.

3 Tested Ways to Make Windows Bootable Again If You Deleted System Partition by Mistake

Here, we mainly introduce 3 ways to restore system: use free third party program, employ diskpart of Windows installation disc, and reinstall Windows without losing personal files.

Trick: please try the first method, then the second one, and the last one. Try the latter only when the former failed to work.


Method 1: Fast Recover System Partition with MiniTool Partition Wizard Bootable Edition


This is the simplest method, and it perfectly worked on our testing machine.

MiniTool Partition Wizard Bootable Edition can help Windows users complete various partitioning operations when Windows is unbootable, including recover lost/deleted partition, rebuild MBR, resize system partition/boot partition, clone disk/partition, and so on.

To use this bootable partition manager to recover partition, you should purchase a paid version. If you are not a Server user, the Professional Edition is available.


After you register the software, you can use the Bootable Media Builder to build the boot CD/DVD discs and boot flash drive. See the guide here: How to Build Boot CD/DVD Discs and Boot Flash Drive with Bootable Media Builder.

Once the bootable disc is created, please start your computer from this disc.

Tip: if you are running Windows via Legacy BIOS + MBR mode, please enter BIOS to set flash drive or CD/DVD as the first boot device. You can google "how to enter BIOS + computer trademark or motherboard mode" for reference. But for UEFI + GPT users, ignore this step.


After successful startup, you can see the window below:

recover system reserved partition select target disk

Here, please select the disk where system partition was originally located and choose "Partition Recovery" function from the left side.

recover system reserved partition set scanning range

Then, set scanning range for the selected disk from 3 ranges and click "Next". If you haven't created new partition after partition loss, you can try choosing Unallocated Space since it costs less time. Otherwise, choose Full Disk.

recover system reserved partition set scanning method

Next, set scanning method for the selected scanning range and click "Next". You can try choosing Quick Scan at first, because it requires much less time. If this method fails to find needed partition(s), go back to this interface again and choose Full Scan.

recover system reserved partition check all needed partitions

Once partitions Partition Wizard detected are listed, please give check marks on all needed partitions and click "Finish" button.

Warning: please check all useful partitions, both existing and lost/deleted, because unchecked partitions will be lost.

recover system reserved partition set system reserved partition active

Then, select the recovered system reserved partition and set it active.

At last, click "Apply" button to make all changes finally performed.

Now, you can try starting computer from Windows side.

Note: remember to set the hard disk where Windows is installed to the first boot device if you are employing Legacy BIOS.


"With MiniTool Partition Wizard Bootable Edition, you can recover the deleted or lost system partition in several simple steps. Show this method to your friends to help them out."

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After recovering system partition, you should be able to boot Windows again. Nevertheless, if this method fails to work, you may need to fix boot, which is our second method.

Method 2: Fix Boot Information with Windows Installation Disc


Tip: we have tested the following methods on virtual machine, which are finally proved to be useful. So, it is worth trying them, but we can't 100% guarantee that they work for you.


To use this method, please prepare a Windows installation disc which had better be the one you used to install Windows. Of course, the one holding the same version as your Windows is also available.

Then, you can start fixing.

However, since there are 2 types of system partitions, namely system reserved partition and EFI system partition, we will show operations separately.

For Legacy BIOS Users


Tip: this method will not create a new system reserved partition but do fix only. So, if you want such a partition, try other methods.


Firstly, please boot computer from the installation media to get the interface below:

recover system reserved partition in diskpart windows setup interface

Then, press on Shift + F10 combination keys to call out Command Prompt, and type following characters.

Trick: every type in Command Prompt as well as Diskpart should end with pressing on Enter key.


In the window of Command Prompt, type diskpart to activate this partitioning tool. Then, type the following commands to set Windows OS partition (C drive most of the time) active:

List disk

Select disk #
(# is the number of the disk where your Windows is installed)

List partition

Select partition #
(here # is the number of the Windows OS partition rather than system reserved partition)

Active

After setting the partition active, please type exit to quit from diskpart.

Then, in Command Prompt please type the following commands to fix boot information:

Bootrec /fixmbr

Bootrec /fixboot

Bootrec /rebuildBCD

The bootrec /rebuilBCD command will search for Windows installations not included in the Boot Configuration Data (BCD) and then ask you if you'd like to add one or more to it. Just type Yes and then Exit to quit from Command Prompt.

Then, you can take out the installation media, and your Windows is very likely to be bootable again.

For UEFI Users


Before fixing boot, please launch MiniTool Partition Wizard Bootable Edition to view partition layout at first. In the section Fast Recover System Partition with Partition Wizard Bootable Edition we have introduced how to create a bootable partition manager, so here we skip this step.


Once the bootable partition manager is created, boot your computer via the disc. Then, MiniTool Partition Wizard will show you disk and partition layout.

If there is no unallocated space for EFI system partition on the left side of C drive, you can shrink your C drive via the Move/Resize Partition function to create one, which could be the size of your original EFI partition or larger. If there is such an unallocated space, skip this step, and just select the very unallocated space, create a FAT32 partition here, and label the partition with efi system.

Tip: we can't format the EFI partition to NTFS, because UEFI firmware does not recognize NTFS.


At last, click "Apply" button to make all changes executed.

After that, you can quit from Partition Wizard bootable disc and start your computer via Windows installation media. Then, press on Shift + F10 combination keys to activate Command Prompt and type the following command:

bcdboot C:\windows

Bcdboot copies boot files from the Windows partition to the EFI system partition and creates the BCD store in the same partition.

Tip: if Windows isn't installed in C drive, please replace C with the letter of your exact Windows OS partition.


Then, you can remove Windows installation disc and restart your computer.

"There are ways to help both Legacy BIOS and UEFI users fix boot information of Windows. Tweet our ways to help more people repair their unbootable Windows."

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Nevertheless, if both recovering system served partition and fixing boot information fail to make your Windows bootable again, you'll need to reinstall Windows.

Method 3. Reinstall Windows without Losing Any Personal Files


How to Reinstall Windows


You can refer to the post How to Reinstall Windows 7 to get some instructions, if you are not very clear of steps to install Windows.

Nevertheless, before doing the reinstallation, please transfer your personal files out from C drive, because reinstalling Windows will erase all its files.

A Pretty Simple Way to Transfer Personal Files out from Unbootable Computer


MiniTool Partition Wizard Bootable Edition can help you complete such an operation. You should buy a corresponding paid edition according to your personal situation. Here, for non-server users, the Professional Edition is available.


Enter the BIOS setting and make your computer boot from the Bootable Edition. And then you will enter its main interface as follows:

backup personal files select C drive

Here, Partition Wizard shows us disk and partition layout.

In this Bootable Edition, each partition letter might be changed compared with those in Windows version, so you need to view their capacity, used space, label, or other features to find the correct partition.


Please make sure there is an unallocated space to hold the copy of C drive. If there is no such unallocated space, shrink an existing partition to create one via the Move/Resize Partition function, and this space should be large enough to hold all contents of C drive. Alternatively, you can connect an external device to hold the copy of partition C. Just connect the device and choose Reload Disk under General tab. Then, the device would emerge in Partition Wizard for you to choose.

Then, select C drive and click "Copy Partition" function from the left side of Partition Wizard main interface.

backup personal files mark a location to save copy of c drive

Afterwards, choose an unallocated space to copy partition C to and click "Next".

backup personal files edit partition

Now you can edit partition size and location, and then click "Finish" to go back to the main window.

backup personal files apply changes

At last, click "Apply" button to make all changes performed.

Once the application is completed, you can reinstall Windows without worrying about losing personal files.

"Tell your friends there is a way to reinstall Windows without losing personal files."

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Your Windows can't boot after deleting system partition? Now, try one of our methods to make it bootable again. Should you have any questions on this post, just feel free to leave us a message in Comment part.