Boot Loader Did Not Load in Hyper-V VM

Why this happened (plain English)​

• Hyper‑V doesn’t like “pass‑through” disks (your USB set as a Physical hard disk). When a pass‑through disk is attached, Hyper‑V can’t make Production/Automatic checkpoints, so it throws that checkpoint error.
• After you disabled checkpoints the VM started, but it can’t find a bootable hard drive. Either:
• there’s a “ghost” pass‑through disk still attached in the VM config, or
• the real OS VHDX isn’t first in the boot order (or isn’t attached), so it falls back to the DVD/ISO and shows Windows Setup.

Fix it step‑by‑step (do this in order)​

• In Hyper‑V Manager > right‑click VM_01 > Settings > SCSI Controller:
• If you see any “Hard Drive” that says “Physical hard disk”, Remove it.
• Still in Settings > Checkpoints: make sure “Enable Checkpoints” is unchecked (at least while we fix this).
• Optional but easy check via PowerShell on the host:
  
  Code:

  Get-VMHardDiskDrive -VMName 'VM_01' |
  ft ControllerType,ControllerNumber,ControllerLocation,Path,DiskNumber

• Rows with a DiskNumber and blank Path = pass‑through. Remove them with:
  Remove-VMHardDiskDrive -VMName 'VM_01' -ControllerType SCSI -ControllerNumber <num> -ControllerLocation <num>

• Settings > SCSI Controller > Hard Drive:
• You should see “Virtual hard disk:” with a Path ending in .vhdx (this is your OS).
• If it’s missing, click Hard Drive > Add > select “Virtual hard disk” > Browse to your OS .vhdx and Apply.

• Settings > Firmware:
• Put “Hard Drive” at the top of the boot list.
• Expand Hard Drive and make sure your OS .vhdx is listed.
• Move “DVD Drive” below Hard Drive, or eject the ISO in the VM window later (Media > DVD Drive > Eject).
• Secure Boot: if this VM runs Windows, set Template to “Microsoft Windows” and leave it enabled.
• Start the VM. It should now boot your OS instead of the installer.

If it still won’t boot​

• Try Startup Repair:
• Mount a matching Windows ISO in Settings > DVD Drive.
• Boot the VM, press a key to boot the ISO, choose Repair your computer > Troubleshoot > Startup Repair.
• If Startup Repair fails, we can rebuild the boot files (one small command). Say the word and I’ll paste kid‑friendly steps.

Safer way to use your USB with Hyper‑V (so this doesn’t happen again)​

• Avoid pass‑through disks. Instead:
• Create a VHDX file on the USB drive (Hyper‑V Manager > Action > New > Hard Disk > VHDX).
• Attach that VHDX to the VM (SCSI > Hard Drive > Add > select the VHDX).
• Inside the VM, initialize/format it once in Disk Management. This works with checkpoints and won’t break boots.

If you get stuck, tell me:​

• A screenshot of the VM’s Firmware page (boot order).
• The output of:
  
  Code:

  Get-VMHardDiskDrive -VMName 'VM_01' |
  ft ControllerType,ControllerNumber,ControllerLocation,Path,DiskNumber

  With those two, I can give you exact “click here, type this” instructions.

• Inside the VM, initialize/format it once in Disk Management. This works with checkpoints and won’t break boots.

Short answer​

Do it safely (kid‑simple steps)​

• In Disk Management inside the VM, only work on the disk whose size matches your new VHDX. Don’t touch anything else.
• Don’t mount the same VHDX on the host while it’s attached to the running VM. One at a time.
• If you need multiple partitions, you can either create several VHDX files or make multiple partitions inside one VHDX.

How to get your existing files into the VHDX​

• Easiest: Copy them in from the host via a share (right‑click the USB drive on the host > Share… > give Everyone read/write > in the VM, open \<host‑PC‑name>\<share>).
• Or temporarily detach the VHDX from the VM, right‑click the .vhdx on the host > Mount, copy files into it, then Eject and re‑attach it to the VM.

• On the host, leave the USB online. In each partition, create a VHDX (e.g., E:\Work.vhdx, F:\Photos.vhdx). Pick a size a bit larger than the data you’ll move there; “Dynamically expanding” is fine.
• Attach each VHDX to the VM (Settings > SCSI > Hard Drive > Add), boot the VM, then inside the VM initialize/format the new disks (NTFS is best).
• Copy your data into the VHDX:
  • Easiest: Share the USB folder from the host and copy inside the VM from \HostName\Share to the new VHDX drive(s).
  • Or do it on the host: Detach the VHDX from the VM, right‑click the .vhdx > Mount, copy files in, then Eject and re‑attach to the VM.
• To preserve timestamps/permissions (optional), use on the host or in the VM:
  robocopy "E:\OldPartitionRoot" "X:\" /E /COPY:DATSO /DCOPY:T /R:1 /W:1
  Replace X: with the mounted VHDX’s drive letter.

• Don’t mount a VHDX on the host while it’s attached to a running VM.
• Make sure there’s enough free space in each USB partition for the VHDX file plus growth.
• This is perfect for data partitions. If any USB partition was bootable or BitLocker‑encrypted and you need it exactly as‑is, say so—we’d use a partition‑to‑VHDX capture (e.g., Disk2VHD) instead of file copy.

Short answer​

Pick one of these paths​

• Attach the VHDX to the VM.
• Boot the VM, then in the VM’s Disk Management: initialize/format the new disk.
• Share the USB folder on the host and copy files from \HostName\Share into the new VHDX drive inside the VM.

• Do not have the VHDX attached to a running VM.
• On the host, right‑click the .vhdx > Mount.
• If first time, initialize/format it in the host’s Disk Management.
• Copy your folders into the mounted VHDX drive letter.
• Eject the VHDX, then attach it to the VM.

• Never mount a VHDX on the host while it’s attached to a running VM.
• You can initialize/format either in the VM (Option A) or on the host (Option B)—not both, and not simultaneously.
• Repeat the same process for each partition’s VHDX.