How to Fix Unmountable Boot Device

The UNMOUNTABLE_BOOT_VOLUME error, with a stop code STOP: 000000ED, has been plaguing users of Windows for a while. The problem is that if Windows can’t identify and interface with the hard disk’s controller, or maybe if the controller is online successfully, but Windows can’t read the volume, you will get this BSOD and error. Simply said, it is an indication that the boot filesystem failed to mount, and Windows can’t read or load the dependencies it needs from it.

Windows is based off a microkernel-like structure, and it can load components and dependencies as it needs. However, there is a basic list of them which absolutely must be loaded during boot, or Windows will fail to boot. This list has been severely shortened with later versions of Windows, and consists of the most basic drivers, and the hard disk controller.

Symptoms of this error may be a failed/incompatible hard disk controller driver, a result of a moved or resized Windows partition, or an attempt to load Windows from the wrong partition. In the first situation, this means that Windows can’t load and read the basic dependencies. This most commonly happens when the hard disk’s controller driver has failed to upgrade or update. The other situations happen when the boot.ini file is incorrectly configured, and it tells the kernel to load from the wrong partition. The partition that boot.ini references to may no longer be the correct one, and you’ll get the BSOD.

Fortunately, there are a couple of things that you can do if you want to handle this situation and make sure it doesn’t happen again. They all require some kind of technical knowledge, and some even an installation drive. Make sure you are careful, and if the other methods don’t work, make sure you have the installation drive at hand before beginning.

Method 1: Change the AHCI/RAID/IDE mode in your BIOS

If this error is caused by a change in the controller’s mode, the fix is very simple. All you have to do is enter the BIOS and change it yourself. The exact situation is different depending on your specific BIOS, but the basic instructions are as follows:

  1. Reboot your device. Immediately before Windows loads, press ESC, F2, F10, F12, or Backspace. The exact button to press depends on your manufacturer, and you can see it briefly during the boot screen, before Windows starts loading.
  2. Once you’re inside the BIOS, look for SATA Configuration or SATA Mode. You should be presented with a few options, most likely IDE, RAID or AHCI. RAID is usually given when there are multiple storage devices on your computer, so don’t worry if you don’t see it.
  3. This part is pretty much trial and error. You should try all of these options, and Save your changes, then Exit, for each one of them. You should try this until you find the setting that lets you boot into Windows.

Method 2: Use System Restore to roll back the disk controller drivers

This is the method that requires your installation media. System Restore is used to roll back to a previous state of Windows, where you’re sure that everything worked properly. This can save you in case a driver or controller update goes wrong and you can’t boot your computer anymore.

  1. Insert your installation media (CD or USB). When your computer is booting, press any key as soon as you see Press any key to boot from CD or DVD.
  2. Once you’ve booted from the media, choose Repair your computer. If you’re using Windows 10, you will have to go to Troubleshoot, then Advanced options, and finally System Restore.
  3. From the menu, you should have a list of System Restore points, and a short description of why they were added. Choose one you know worked well, and choose Next to continue. Follow the wizard’s instructions to complete the process. If everything is okay, it should work just fine now.

Method 3: Fix the file system with CHKDSK

Another possible cause of this issue is a damaged file system which cannot be mounted. Fortunately, Windows comes with nifty built-in tools that may help in a situation like this. However, if you’re unable to boot, you will have to use steps 1 and 2 of the previous method. However, instead of System Restore, you will need Command Prompt.

  1. Once you’re in the command prompt, type in chkdsk /r , and press Enter to execute the command. Give it enough time to run, and only proceed once it’s done.
  2. Type in exit and press Enter to execute once the previous command is done. This will restart your computer, and it may take a little longer to boot, but you should have it up and running once it’s done.

Method 4: Fix the Master Boot Record

A malfunctioning Master Boot Record (MBR) can cause this problem as well. The MBR identifies where and how your OS is located. The solution is, once again, with the Command Prompt from an installation media. Use the steps from the previous methods to access it. When you get to the Command Prompt, type in bootrec /fixboot and press Enter to execute the command. You should wait for the process to complete, and then reboot your computer. It should boot up just fine.

Method 5: Use automatic repair

Automatic Repair is another built-in tool that you can try. It is accessed from the same Recovery menu like the Command Prompt and the System Restore menus.

  1. Once you’re in the menu, choose Startup Repair.
  2. Choose your operating system. The repair starts immediately, and you should give it time for it to complete. Once it’s done, your OS should boot just fine.

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