Windows won’t start

New drive won't boot after cloning from the old one

After cloning Windows from an old hard drive to a new SSD, the PC won't boot from the new drive, either showing an error or failing silently, even though the clone process reported success.

Difficulty
Advanced
Time
30–90 minutes
DIY cost
$0
Pro cost
$80–$180

Symptoms

  • Clone completed without reported errors
  • New drive doesn't appear as bootable, or Windows fails to load from it
  • May show boot errors like BOOTMGR missing or inaccessible boot device
  • Old drive still boots fine if reconnected

Likely causes

  • CommonBIOS still pointed at the old drive or wrong boot modeThe boot order needs to be updated to select the new drive after cloning.
  • CommonCloned drive using a different partition style (MBR vs GPT) than BIOS expectsA mismatch here prevents the new drive from being recognized as bootable.
  • PossibleCloning software didn't correctly clone the small boot/recovery partitionsSome cloning tools miss the hidden partitions Windows needs alongside the main one.
  • PossibleDrive connected to an incompatible port for booting (like an external USB enclosure for an internal-only setup)Some BIOS versions don't support booting Windows from certain USB-connected drives.
  • Less commonOld drive still connected causing boot conflictsHaving both drives connected can confuse which one BIOS or Windows tries to boot from.

What to do

  1. Enter BIOS/UEFI setup and check the boot order; explicitly select the new drive as the first boot device if it's listed.
  2. Confirm whether BIOS is set to UEFI or Legacy/CSM mode, and that it matches the partition style of the new drive (most modern SSDs and Windows installs use GPT with UEFI).
  3. If only the old drive is bootable, temporarily disconnect the old drive and try booting from just the new one to avoid conflicts.
  4. Boot from a Windows installation USB, choose Repair your computer, and run 'bootrec /fixmbr', 'bootrec /fixboot', and 'bootrec /rebuildbcd' targeting the new drive.
  5. Check that the new drive is installed internally on the same type of interface (SATA or NVMe) as intended for regular booting, not left in a USB enclosure if that's not supported for boot on your BIOS.
  6. If the clone missed hidden partitions, some cloning software has a 'clone disk' rather than 'clone partition' mode; consider recloning using the full-disk option.
  7. If repeated attempts fail, a clean Windows install on the new drive, followed by reinstalling programs, is often more reliable than repairing a problematic clone.

Tools and parts

  • Bootable Windows installation USB drive

When to call a pro

If boot repair commands and boot order changes don't get the cloned drive booting, a technician experienced with drive cloning can diagnose partition table or firmware mode mismatches.

Safety

Generally low risk

Generally low risk for a careful person. Stop if anything looks different from what this guide describes.

Related guides

Operator provides AI-generated troubleshooting information. It can be wrong. For safety-critical, electrical, gas, structural, medical, automotive safety, or other high-risk problems, consult a qualified professional.