@Vishwanth 

When you reset or clear the Secure Boot keys in a Dell BIOS, the active database (db, KEK, and PK) is either cleared completely or reverted to a state where the active certificates no longer match or validate your Windows Boot Manager (bootmgfw.efi) . Because the BIOS cannot cryptographically verify the signature, it halts execution and reboots .

Restore Factory Secure Boot Keys in BIOS
Resetting the keys via the Custom Mode / Expert Key Management interface in Dell BIOS often requires turning off Custom Mode to restore the factory default NVRAM databases .

Power on the machine and tap F2 to enter BIOS Setup .
Navigate to Secure Boot (or Boot Configuration / Security on newer Dell BIOS interfaces) .
Locate Expert Key Management: If Enable Custom Mode is turned ON, select Reset All Keys. Then toggle Enable Custom Mode to OFF / Disabled . On Dell firmware, disabling Custom Mode restores the factory-embedded Microsoft PCA and Dell platform keys to the active database .
Under Secure Boot Enable, set it to Enabled (or set Secure Boot Mode to Deployed Mode if prompted) .
Click Apply Changes and Exit .

Re-deploy the Microsoft Secure Boot Recovery Utility
If Windows updated its bootloader signatures (for example, rolling out updated Microsoft Windows Production PCA 2011/2023 certificates) and the motherboard's factory keys are out of sync, Windows provides a native recovery binary .
Turn Secure Boot OFF in BIOS and boot into Windows .
Insert a USB flash drive and format it as FAT32 .
Open File Explorer, navigate to:
text
C:\Windows\Boot\EFI\
Locate the file named securebootrecovery.efi .
On the USB drive, create a folder structure: EFI\Boot\ .
Copy securebootrecovery.efi into the EFI\Boot\ folder and rename it to bootx64.efi .
Restart the computer, tap F12 at the Dell logo, and select the USB drive under the UEFI boot menu .
The screen will display Microsoft Secure Boot Recovery and automatically update the NVRAM certificates before restarting . After it restarts, enter the BIOS (F2), turn Secure Boot ON, and boot normally .

Rebuild the EFI System Partition (BCD and Boot Files)
If the signatures in your current EFI System Partition are mismatched, rebuilding the EFI partition from within Windows will reinstall cleanly signed bootloaders.
Boot into Windows (with Secure Boot disabled) .
Press Win + X and select Terminal (Admin) or Command Prompt (Admin).
Mount the EFI partition by running:
text
mountvol S: /s
Reinstall and refresh the boot files from your local Windows installation to the EFI system partition:
text
bcdboot C:\Windows /s S: /f UEFI
Unmount the partition:
text
mountvol S: /d
Restart the PC, enter BIOS (F2), re-enable Secure Boot, and verify if Windows boots .

Perform a Full NVRAM / RTC Reset
If the BIOS is holding corrupt key tables in non-volatile memory, standard BIOS flashing or .rcv recovery files will not overwrite them .
Shut down the computer and disconnect the power adapter .
Press and hold the power button for 30 to 35 seconds (on modern Dell laptops and desktops, this triggers an RTC / Real-Time Clock hardware reset).
The power LED will flash amber/white several times to signal a full CMOS/NVRAM wipe.
Power on, tap F2, enable Secure Boot, and ensure storage settings match your original setup .