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Updated Oct 2021

Secure Boot Is On but Windows Will Not Start? Here Is the Fix

Written byMohammad Shojib Ahmed · 7 min read

Why your PC returns to the BIOS after enabling Secure Boot, how to confirm an MBR drive, and two ways to fix it, with or without keeping your files.

NextMotion / Tech tutorials

Guide + video

Key takeaway

An MBR drive cannot boot with Secure Boot. Convert it to GPT and the boot loop stops.

In this article7 sections · 7 min read
  1. Why it happens
  2. Step 1: Get back into Windows
  3. Step 2: Confirm the drive is MBR
  4. Fix 1: Keep your files (recommended)
  5. Fix 2: During a fresh Windows install
  6. Other causes if your drive is already GPT
  7. The short version

The video plays from YouTube when you press play.

You enable Secure Boot, restart, and instead of Windows you land back in the BIOS. Again and again. Turning Secure Boot off makes Windows start, but that is not a fix if you need Secure Boot for Windows 11 or for Valorant's Vanguard anti-cheat.

In almost every case I have seen, the cause is the same: the Windows drive uses the old MBR partition style. Here is why that breaks Secure Boot, how to confirm it and the two ways to fix it.

Why it happens

Secure Boot only works when the PC starts in UEFI mode. UEFI can only start Windows from a drive that uses GPT (GUID Partition Table). Older Windows installs often use MBR (Master Boot Record) instead.

When you turn on Secure Boot, the board switches to pure UEFI. It looks at your MBR drive, finds nothing it is allowed to start and sends you back to the BIOS. Windows is still there, untouched. The PC just cannot reach it in this mode.

Why the PC loops

The chain that breaks

01Secure Boot onThe board switches to pure UEFI.You
02UEFI looks for GPTIt only starts GPT drives.Firmware
03Drive is MBRNothing it is allowed to start.The cause
04Back to the BIOSConvert to GPT to break the loop.The fix

Step 1: Get back into Windows

Open the BIOS, turn Secure Boot off again, or set the boot mode back to CSM or Legacy, and save. Windows will start normally. You need to be in Windows to check the drive and to use Fix 1 below.

Step 2: Confirm the drive is MBR

  1. Right-click Start and open Disk Management.
  2. Right-click the disk Windows is on, usually Disk 0, and choose Properties.
  3. Open the Volumes tab and look at Partition style.

If it says Master Boot Record (MBR), that is your problem, and the fixes below will solve it. If it already says GUID Partition Table (GPT), skip to the section on other causes.

If Windows is already installed and you want to keep everything, convert the drive in place with Windows' own MBR2GPT tool. It rewrites the drive's map without touching your files. I walk through it step by step in how to convert MBR to GPT without data loss.

After the conversion, switch the BIOS to UEFI, then enable Secure Boot again. Windows will start normally.

Fix 2: During a fresh Windows install

If you are installing Windows from scratch anyway, you can convert the drive to GPT during setup with a tool called diskpart.

Warning: This method erases the selected disk. Only use it on a drive you are about to install Windows on, and double-check the disk number.

  1. Boot from your Windows USB. On the first setup screen, press Shift + F10 to open Command Prompt.
  2. Type diskpart and press Enter.
  3. Type list disk. Disks that already use GPT have an asterisk (*) in the Gpt column. Use the Size column to identify your target drive.
  4. Type select disk 2, using your own disk number.
  5. Type clean to wipe the disk, then convert gpt.
  6. Type list disk again. Your disk now has the asterisk.
  7. Type exit, close Command Prompt, click Refresh in setup, select the unallocated space, click New and continue the installation.

Once Windows is installed on the GPT drive, enable Secure Boot and the PC will start normally.

Fix 2 · diskpart

The commands, in order

  • Shift + F10
  • diskpart
  • list disk
  • select disk
  • clean
  • convert gpt
01list diskFind your drive by its sizeLook
02select disk 2Use your own disk numberCheck twice
03clean, then convert gptErases the disk and makes it GPTErases data

Only for a fresh install. Fix 1 keeps your files.

Other causes if your drive is already GPT

  • CSM is still on: some boards keep a legacy option active. Set the boot mode to UEFI only, or set CSM to Disabled.
  • The Secure Boot keys are missing: choose Enroll all Factory Default Keys, or Install default keys, in the Secure Boot menu.
  • The wrong boot entry is first: in the boot order, choose Windows Boot Manager, not the drive name on its own.
  • A non-Windows boot device is attached: unplug USB drives and extra disks and try again.

The short version

A PC that keeps returning to the BIOS after you enable Secure Boot almost always has an MBR drive. Turn Secure Boot off to get into Windows, confirm the partition style, convert the drive to GPT with MBR2GPT, switch to UEFI and turn Secure Boot back on.

Mohammad Shojib AhmedFounder & Creative Lead at NextMotion. A multidisciplinary creative and YouTube educator sharing practical knowledge on technology, digital tools and visual storytelling.

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