The most common ending to an MBR2GPT story: conversion succeeds, the PC reboots into Legacy mode out of habit, and a GPT disk flatly refuses to boot that way. One firmware setting fixes it.
MBR2GPT ends its run with a warning that is easy to click past: after conversion, you must configure the firmware to boot in UEFI mode. This is not fine print. A GPT system disk can only be booted by UEFI firmware — the old Legacy/CSM path looks for boot code in the MBR, and your disk does not have a working one of those any more. This page is the switch itself, what the failure looks like if you skip it, and the verification that closes the job.
👆 These messages mean the firmware cannot find a Legacy boot path — on a freshly converted disk, that is expected until you switch modes
Legacy booting and UEFI booting are two different handshakes. Legacy firmware reads the master boot record and chain-loads from an active partition — the world your disk just left. UEFI firmware instead reads the EFI System Partition that MBR2GPT created and starts the Windows Boot Manager from a file on it. Until the firmware is told to use the second handshake, it will keep attempting the first one and reporting, accurately, that there is nothing for it to boot.
Nothing about your data is involved in this failure. The disk is converted, Windows is intact — the doorbell is simply wired to the old door.
With the machine now in UEFI mode, Secure Boot can be enabled — and if this conversion was preparation for Windows 11, you will want it, since Windows 11 requires UEFI firmware with Secure Boot capability. Enable it after Windows has booted successfully once in plain UEFI mode, so that if anything complains you know which change caused it. One change at a time, even at the finish line.
msinfo32. The BIOS Mode line should read UEFI.Both lines changed means the job is genuinely complete — disk converted and firmware converted.
Then the hardware has told you the truth Microsoft's documentation starts with: the device must support UEFI before you convert. On a Legacy-only board, a GPT system disk will never boot, and the recovery route is your backup — restore the disk image you made before converting, returning the machine to its working MBR state. This is the one scenario where the backup graduates from precaution to rescue, and it is exactly why the check belongs at the start of the main guide, not in this page's hindsight.
The closing minutes of the video are this exact firmware screen — watch them before your reboot, not after the black screen.
▶️ Watch Full VideoNo — this message almost always means the firmware is still in Legacy/CSM mode. Enter setup, switch the boot mode to UEFI, save, and the same disk will boot Windows normally.
It appears as an entry once the firmware is in UEFI mode and can see the EFI System Partition MBR2GPT created. If the mode is UEFI but the entry is missing, re-check that the conversion truly completed successfully, and that you are looking at the disk you converted.
Do it as a separate, second step. Boot once in UEFI mode first and confirm Windows starts; then enable Secure Boot. If a problem appears, you will know which of the two changes caused it.