PC won’t boot after cloning

The clone went well, the SSD is fitted, and the PC will not boot. In the vast majority of cases, Windows is intact: it is the boot that is stuck. Here are the causes, from the most common to the rarest.

What you see

“No bootable device”, “Reboot and select proper boot device” or “Operating system not found”;
a black screen with a cursor, or straight back to the BIOS;
an “INACCESSIBLE_BOOT_DEVICE” blue screen;
“Automatic Repair” running in a loop;
a request for the BitLocker recovery key.

1. The boot mode is wrong

This is the number one cause. A GPT disk only boots in UEFI mode, an MBR disk only in Legacy mode (CSM). If the clone changed format, or if the BIOS was reset, the PC finds nothing.

Check the new disk’s format (Disk Management on another PC, or list disk in diskpart), then set the BIOS: UEFI with CSM disabled for a GPT disk, Legacy or CSM enabled for an MBR disk.

2. The PC boots from the wrong disk

The old disk is still connected, or the BIOS kept the old boot order. Two identical disks connected at the same time also cause trouble: Windows sees the same signature twice and takes one of them offline.

For the first boot, disconnect the old disk. In the BIOS, put “Windows Boot Manager” (or the new SSD) first.

3. The boot files are missing

Some tools only copy the C: partition; others stop before writing the boot files. Windows is there, but nothing starts it.

If the disk does have its small boot partition (FAT32 of 100 to 300 MB for a GPT disk, “System Reserved” for an MBR disk), the files can be recreated from a Windows installation USB drive. Boot from the USB drive in the same mode as the disk (UEFI for a GPT disk), then press Shift+F10 on the setup screen to open the command prompt:

diskpart
list volume
exit
bcdboot D:\Windows

list volume is used to find the letter of the Windows volume: from the USB drive, it is often not C:. Replace D: with the letter you found. This is the repair Microsoft describes for BCDBoot: the tool copies the boot files from Windows, in the format of the mode the USB drive booted in.

If this small partition does not exist at all, it has to be created first, which means shrinking C:. The simplest option is then to redo the clone with a tool that rebuilds the whole disk.

4. The SATA mode was changed in the BIOS

An “INACCESSIBLE_BOOT_DEVICE” blue screen just after cloning often comes from a changed SATA setting (AHCI or RAID, Intel RST or VMD on recent laptops). Windows boots with the driver for the mode it knew. Put the previous setting back.

5. Secure Boot refuses to boot

A “Secure Boot Violation” message or a silent refusal can come from a boot loader that the BIOS no longer recognises, since Microsoft’s security revocations. Update Windows and the BIOS. When troubleshooting, disabling Secure Boot just long enough to boot lets you confirm that this is the cause.

6. BitLocker asks for the key

This is not a fault: the boot has changed, and the PC’s security chip notices it. Type the customer’s recovery key once, and Windows starts. The customer can find it at account.microsoft.com/devices/recoverykey, or get it from their IT department. Ask for it before cloning.

7. The clone was interrupted

A power cut or a cable pulled out during the copy leaves an incomplete disk, even if it looks full. Do not repair it: redo the clone.

How MBI Clone avoids these failures

The boot is rebuilt on the new disk, in UEFI or BIOS mode according to the chosen format, then read back with the partition table, Windows and the recovery environment before the end.
An interrupted clone never boots: its boot files are only put in place after the final check, and MBI Clone flags the disk the next time it starts.
The end of the clone tells you which mode to set in the BIOS: “set the BIOS to UEFI mode (Legacy/CSM disabled if needed)”, or “leave the BIOS in Legacy (CSM) mode”.
When it can read them, the PC’s Secure Boot certificates are checked before cloning.
The new disk is taken offline at the end, so that it does not get mixed up with the old one on the workshop computer.

Common questions

Does Windows need to be reinstalled?

Almost never. In the cases above, Windows is intact: only its boot needs to be set or rebuilt.

The PC booted with the old disk, so why not with the new one?

Because the BIOS looks for the boot files in a specific place, which is different in UEFI and in Legacy mode. A disk cloned in the other format, or without its boot partition, is not found.

What should I do with the old disk?

Keep it as it is until the new one has booted and the customer has found everything they need.