What Should I Do After Accidentally Marked Drive C Active [New]

Sherly updated on Jan 19, 2024 | Home >Computer Instruction

If your PC cannot boot after your accidentally marked drive c active, and you are wondering what to do to mark the correct system partition active, this article is for you. Here, we will discuss what happens if you accidentally marked drive c active, System and boot partition, and what partition should be active.

First, let us know what happens if you mark c drive as active. You will get an error message saying "Unable to load MBR" while trying to boot your PC. The only time if the correct partition with the boot files is active, then the MBR will load the boot files and starts the PC for further use.

In the next section, we will learn what partitions exist on the PC, what they do, and which should be active to rectify such errors.

Which Partition Should Be Active

Before moving on to how to set the system partition to active, let us learn about the system and boot partition and how they boot your PC. We will learn about their differences and functioning.

In the older versions of the OS, both the system partition and boot partition were present in the same partition, and it is in drive C. Since Windows 7, they can be either merged or separated. For every OS, a system and boot partition exists on your PC, and if more than one OS exists, then multiple systems and boot partitions may exist.

Guide on System Partition and Boot Partition

So if we install Windows OS on a never used hard disk, the System and boot partitions will be separate. The partition with the System reserved data (500MB for Windows 10, 350MB for Windows 8, and 100MB for Windows 7) in Disk Management is the system partition, and the C drive is the boot partition, as seen in the picture.

Now there is a System Reserved partition, and there can be only one system partition on the respective disk, irrespective of how many operating systems are installed. All the boot programs for the installed Windows OS will be automatically saved to this system partition with multiple boot partitions on other drives.

In a simple way, the partition containing boot programs like BOOTMGR and BCD or NTLDR and boot.ini is called a System partition. And this System partition should be active to boot your Windows OS successfully. This partition can be on drive C or separately exist as a System Reserves partition.

If you have multiple Windows OS present on your device, you have multiple system partitions on one disk, and you need to set the required OS version's partition to be active to boot your PC.

Now let us learn what all files or programs the system and boot partition consist of.

System partition mainly holds:

  1. 1. Windows Boot Manager (BOOTMGR) is a part of the boot volume record, which starts your operating System by executing the winload.exe file.
  2. 2. The BCD ( Boot Configuration Database) program, which replaces the boot.ini.
  3. 3. Win RE: The Windows Recovery Environment, labeled System in Disk Management.

Boot partition mainly holds:

As you can see in the Disk Management, the boot partition is our C drive on our PC. It holds all the Windows OS files.

Generally, when you boot your computer, it automatically follows a sequence of operations to boot (reboot) the OS files to turn on your computer. For that, MBR searches the master partition for the active system partition and reads the active system partition, which contains all those files. Then reads the BOOTMGR and passes control to it; BOOT MGR reads the BCD to learn the menu entries and then invokes the winload.exe to load the corresponding kernel and core device drivers to boot the Windows.

Solve Accidentally Marked Drive C Active Issue - 2 Methods

We provide two ways to help you solve this issue, and you can choose one way based on your needs. The two ways are as follows:

Way 1. Solve Accidentally Marked Drive C Active Issue via EaseUS Partition Master

Way 2. Solve Accidentally Marked Drive C Active Issue via Windows Installation Media

To solve the issue and set the correct system partition as active, follow the two methods below.

Way 1. Solve Accidentally Marked Drive C Active Issue via EaseUS Partition Master

EaseUS Partition Master is a partition software with exclusive features to easily manage partitions on hard drives, SSD, and external disks. It provides the "Set Partition as Active" feature. We can set the required system partition on our PC as active in just one click using EaseUS partition Master to save your WIndows from MBR disk boot failure. Download this tool and follow the guide below to try it.

Free Download 

Windows 11/10/8/7100% Secure

Step 1. Run EaseUS partition manager software. On the disk map, right-click the target partition and choose "Advanced".

Step 2. Then, select "Set Active" from the drop-down menu. Click "Yes".  And choose "Execute 1 Task(s)" and click "Apply".

Apart from managing the disk partition, this tool helps free up hard drive space and manage USBs and external hard drives to optimize your disk performance. Download the software and use its user-friendly interface to perform complex operations on your hard drives easily.

Free Download 

Windows 11/10/8/7100% Secure

Way 2. Solve Accidentally Marked Drive C Active Issue via Windows Installation Media

We can use Windows Installation Media to solve the issue if you have a bootable CD, DVD, or USB flash drive. If you need help creating a bootable CD, DVD, or USB flash drive, follow the articles for detailed steps. 

Step 1: Boot the computer via a bootable Windows Installation media like CD, DVD, or USB. Then you need to enter the BIOS settings during the booting process. Every computer has a different key for the BIOS settings.

Step 2: You will be redirected to the installation setup. Set your language and time, and you will see the below screen. Click on "Repair your Computer."

Step 3: Now Troubleshoot > Advanced Options > Command Prompt. Now enter the following commands one by one and hit Enter after each entry.

  • diskpart
  • list disk
  • select disk 2 (2 means the number of the disk you will operate)
  • list partition
  • select partition n (n is the number of the correct system partition)
  • active

set partition active

After completing the commands, reboot your computer to see if it boots normally as before. By the way, there are some other links below you might be concerned about:

The Final Verdict

If you have accidentally marked drive c active, it will create booting problems on your computer. Follow the guide to know the system partitions in detail and how to fix this issue. You can do this easily using the EaseUS partition Master in a single click or follow method 2 to complete this process using BIOS settings manually.

You need to be careful when typing the commands, or data loss may occur. Hence, EaseUS Partition Master is a reliable choice since it can set the boot partition without any data loss. Download this tool to try. You will like what it brings to you.

Free Download 

Windows 11/10/8/7100% Secure

What Should I Do After Accidentally Marked Drive C Active FAQs

Here are some of the most frequently-asked FAQs on the topic. If you have similar queries hope this will help you.

1. What happens if I mark the partition as active?

Generally, the active partition is responsible for loading or booting your computer. It contains all the boot and OS files and is known as a system partition; if you mark it as active, the OS loads and starts your computer, usually located on the computer's local disk.

2. How do I mark a drive as active?

You can either use a professional software tool like EaseUS partition master or manually use the command prompt with the help of Windows Installation Media. Here, you can use the easier method:

Step 1. Download and Launch EaseUS Partition Master.

Step 2. Right-click the target hard drive and choose "Advanced."

Step 3. Select "Set Active" and then click "Execute Task."

3. Should the C drive be an active partition?

Sometimes the System Reserved partition, and sometimes it is the C drive. You can set it as the active partition. The system partition is set to active to boot the computer. Depends on the drive containing the system partition.

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Updated by Sherly

Sherly joined EaseUS in 2022 and she has always loved writing articles and enjoys the fun they bring. She receives professional training here, focusing on product performance and other relative knowledge. She has written over 200 articles to help people overcome computing issues.

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