No Boot Device Found – Dell UEFI/Legacy Boot Mode and GPT/MBR Partition Mismatch
Dell computers display 'No Boot Device Found' or 'No Bootable Device' errors when the BIOS boot mode is switched between UEFI and Legacy without reformatting the drive, because GPT-partitioned drives are incompatible with Legacy/MBR boot mode and vice versa. The fix requires aligning the BIOS Boot List Option and Secure Boot setting with the drive's partition scheme, or reformatting and reinstalling the OS if a mode change is genuinely required. Reverting the BIOS to the original boot mode is the fastest recovery path when no partition change is needed.
Indicators
- System displays 'No Boot Device Found' error after changing boot mode to Legacy in BIOS
- System displays 'No Bootable Device' message on startup
- Computer fails to boot after switching from UEFI to Legacy mode
- OS installation fails or is not detected when booting in Legacy mode
- Boot Sequence list is empty after Legacy mode is selected
- System previously booted normally under UEFI but fails to boot after BIOS mode change
Likely causes
- Hard drive is partitioned with GPT, which is incompatible with Legacy/MBR boot mode
- Hard drive is partitioned with MBR, which is not recognised by UEFI Secure Boot
- Boot mode was changed from UEFI to Legacy in BIOS without reformatting the drive to MBR
- OS was installed under UEFI mode but the system is now configured to boot in Legacy mode
- Secure Boot is still enabled while Legacy mode is selected, blocking all boot devices
- Incorrect or empty boot sequence order after boot mode was changed
Diagnostic steps
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Restart the computer and press F2 repeatedly at the Dell splash screen to enter BIOS/UEFI Setup.
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Navigate to the Boot tab and note the current Boot List Option (UEFI or Legacy). Also check whether Secure Boot is enabled or disabled under the Security or Boot tab.
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Review the Boot Sequence list. If it is empty, the drive's partition table is likely incompatible with the currently selected boot mode.
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If the system can be booted temporarily by reverting to UEFI mode, open a Command Prompt and run 'diskpart', then type 'list disk'. A GPT drive shows an asterisk (*) in the GPT column; no asterisk indicates MBR.
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Alternatively, open Disk Management (diskmgmt.msc), right-click the system disk, and select Properties. The Volumes tab shows the Partition Style as GPT or MBR.
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If the drive is GPT and UEFI mode is acceptable, revert the BIOS Boot List Option to UEFI, ensure Secure Boot is enabled, save and exit — this is the fastest resolution.
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If Legacy mode is genuinely required and the drive is GPT, back up all data, reformat the drive as MBR using diskpart ('clean', then 'convert mbr'), and reinstall the OS using Legacy/MBR-compatible boot media.
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If switching to Legacy mode, disable Secure Boot in BIOS before saving changes. Set Boot List Option to 'Legacy', save and exit, then boot from MBR-compatible installation media.
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After OS reinstallation or BIOS revert, confirm the system boots successfully and verify the boot sequence is correct in BIOS.
Resolution path
- Enter Dell BIOS Setup by pressing F2 at startup
- Identify current Boot List Option (UEFI or Legacy) and Secure Boot status
- Determine the system drive's partition style (GPT or MBR) using diskpart or Disk Management
- Fast path — UEFI mode acceptable: revert Boot List Option to UEFI, enable Secure Boot, save and reboot
- Legacy mode required with GPT drive: back up all data, boot from recovery media, reformat drive to MBR using diskpart ('clean' then 'convert mbr'), reinstall OS using Legacy/MBR boot media
- Disable Secure Boot in BIOS before saving if Legacy mode is selected
- Ensure Boot List Option matches the drive partition style (UEFI=GPT, Legacy=MBR)
- Save BIOS settings, reboot, and confirm the system boots successfully
Prevention
- Do not change the BIOS boot mode (UEFI/Legacy) after OS installation without first reformatting the drive and reinstalling
- Ensure the drive partition style (GPT for UEFI, MBR for Legacy) matches the intended boot mode before OS installation
- Prefer UEFI mode with GPT on modern Dell systems unless Legacy compatibility is explicitly required by software or hardware constraints
- Document the boot mode and partition scheme used during OS deployment for each device for future reference
- Keep Secure Boot enabled when using UEFI mode to maintain boot integrity and prevent unauthorised modifications
- When creating bootable USB installation media, match the media boot mode to the target boot mode (UEFI or Legacy/MBR)
Tools
- Dell BIOS/UEFI Setup (F2 at boot)
- diskpart (Windows Command Prompt utility)
- Windows Disk Management (diskmgmt.msc)
- Windows bootable installation media (USB/DVD, UEFI or Legacy as required)
- Dell ePSA / SupportAssist Pre-boot Diagnostics (F12 at boot)