Bootcamp Partition won't boot or mount.

I have an issue with Bootcamp, i am using a late 2012 21.5-inch iMac running Catalina version 10.15.17, i used Minitool Partiton Wizard on the Windows side to change the partition sizes, but now my bootcamp partition won't boot and i haven't been able to fix it myself. I tried to follow this post and others that Loner T responded to but i could not advance. As seen in the screenshots my bootcamp partition is unmounted and won't mount though disk utility. the disk0s3 used to be the unused space in my bootcamp partition. i would like to use my windows partition again normally, as I enjoyed the option to switch between MacOS and Windows.

Posted on Jun 3, 2026 7:27 PM

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Posted on Jun 7, 2026 1:46 AM

I don't know if this will help, but can you boot from any external Windows media? If you can, you might be able to run a check on the filesystem. To do this, you'll need a valid Windows install stick and to be able to boot to it. Plug the stick into a USB port and hold Option as you restart the Mac. If everything's in order, you'll see a graphical list of volumes. You want the one labeled "Windows" on a USB drive. Click the arrow below it, and quickly strike a key as the screen switches to Windows. If this is successful, you'll be in Windows Setup. Here, click "Repair your computer" at the bottom.


You might see s blue screen with a slew of buttons. Click "Advanced options", then "Command Prompt"


If your SSD has BitLocker, you'll need the long key sequence from your Microsoft account to open the volume for access (BitLocker is on by default under certain conditions).


At the Command Prompt, write:


chkdsk <x>: /f


where x is a letter from C onward that represents the Windows volume. Finding the actual letter is a little tricky. Let's say it's D, so you'd write:


chkdsk d: /f


Hit Return when you finish, and CHKDSK will examine and fix (that's our /F switch) the data structures on the volume. The time required is directly proportional to the amount of data that should be on the volume. You'll see some additional output for each problem found and fixed. Let it continue until the Command Prompt returns.


Restart your Mac and if it finds Windows, try to start it. If you can get to the Desktop, you're good to go. If not, you'll have to try other avenues, including redoing Boot Camp.


Nate

9 replies
Question marked as Top-ranking reply

Jun 7, 2026 1:46 AM in response to dummyminion

I don't know if this will help, but can you boot from any external Windows media? If you can, you might be able to run a check on the filesystem. To do this, you'll need a valid Windows install stick and to be able to boot to it. Plug the stick into a USB port and hold Option as you restart the Mac. If everything's in order, you'll see a graphical list of volumes. You want the one labeled "Windows" on a USB drive. Click the arrow below it, and quickly strike a key as the screen switches to Windows. If this is successful, you'll be in Windows Setup. Here, click "Repair your computer" at the bottom.


You might see s blue screen with a slew of buttons. Click "Advanced options", then "Command Prompt"


If your SSD has BitLocker, you'll need the long key sequence from your Microsoft account to open the volume for access (BitLocker is on by default under certain conditions).


At the Command Prompt, write:


chkdsk <x>: /f


where x is a letter from C onward that represents the Windows volume. Finding the actual letter is a little tricky. Let's say it's D, so you'd write:


chkdsk d: /f


Hit Return when you finish, and CHKDSK will examine and fix (that's our /F switch) the data structures on the volume. The time required is directly proportional to the amount of data that should be on the volume. You'll see some additional output for each problem found and fixed. Let it continue until the Command Prompt returns.


Restart your Mac and if it finds Windows, try to start it. If you can get to the Desktop, you're good to go. If not, you'll have to try other avenues, including redoing Boot Camp.


Nate

Jun 6, 2026 7:52 PM in response to dummyminion

dummyminion wrote:
Ok, here are the results of the commands.
sudo gpt show disk0
Password:
gpt show: unable to open device 'disk0': Operation not permitted
sudo gpt show -l disk0
gpt show: unable to open device 'disk0': Operation not permitted
It seems a little weird that the last two commands won't show much, not sure what that's about. Thanks for being patient.

That is disappointing. It seems the Catalina version of the "gpt" utility won't work on the currently booted drive (it does with a later version of macOS & this utility).


There is a possibility we can fix the drive while booted into Recovery Mode (Command + R) or from a bootable macOS Catalina USB installer. You can try running these commands again while booted in Recovery Mode or from a USB Catalina installer. I'm hopeful the output of those "gpt" commands will be enough to fix things.


Jun 4, 2026 6:42 PM in response to dummyminion

Unfortunately I have not seen @LonerT here for some years now, I really enjoyed their knowledge in this area.


I need to review some of @LonerT's posts as well as checking out the current utilities to see if I can assist you. I recently experimented with manually resizing Linux partitions so I understand the basics, but some of the utilities available for macOS can be difficult to work with since they seem so clumsy to use. I'll see if I can find some time tomorrow or over the weekend to experiment a bit.


In the mean time, please post the output for the following Terminal commands:

diskutil  list  internal


sudo  gpt  show  disk0 


sudo  gpt  show  -l  disk0


FYI, the " -l " for the last command is a lower case letter "L".


The commands which begin with "sudo " will prompt you for your macOS admin password. Nothing will appear on the screen as you type the password. Press the "Return" key to submit the password. If you execute those commands beginning with "sudo" within about 15 minutes of each other, then you won't be prompted for the password the 2nd command.


FYI, if you copy & paste the command & output here.......using the "Code Insertion" tool whose icon looks like "</>" on the forum editing toolbar will usually make the Terminal output easier to read & it helps to separate out the conversation from the data. Or provide a screenshot of the Terminal window.

Jun 8, 2026 6:58 AM in response to dummyminion

dummyminion wrote:
Im in recovery mode right now but the terminal seems to be in bash and cant find the commands that start in sudo. The first command comes out identical to when i ran it normally.

I'm sorry about that. While booted into recovery mode or from a USB installer, you must omit the "sudo " part of the command since you are already at a prompt with administrator (aka "root") privileges.

Jun 6, 2026 6:49 PM in response to HWTech

Ok, here are the results of the commands.

diskutil list internal
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                 Apple_APFS Container disk1         209.8 GB   disk0s2
   3:       Microsoft Basic Data BOOTCAMP                501.0 GB   disk0s3

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +209.8 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume Untitled - Data         28.8 GB    disk1s1
   2:                APFS Volume Preboot                 24.6 MB    disk1s2
   3:                APFS Volume Recovery                526.8 MB   disk1s3
   4:                APFS Volume VM                      4.3 GB     disk1s4
   5:                APFS Volume Untitled                11.2 GB    disk1s5



sudo  gpt  show  disk0
Password:
gpt show: unable to open device 'disk0': Operation not permitted


sudo  gpt  show  -l  disk0
gpt show: unable to open device 'disk0': Operation not permitted

It seems a little weird that the last two commands won't show much, not sure what that's about. Thanks for being patient.

Bootcamp Partition won't boot or mount.

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