DELL VOSTRO 3515 - AFTER WINDOWS UPDATE UNABLE BOOT

Question

Our company has a batch of DELL Vostro 3515 laptops purchase in year 2021, and some of them are unable to boot after performing the Windows Update on 11 May 2026. The error message displayed is: “Windows Boot Manager has been blocked by the current security policy.”

We have already entered the BIOS and restored the default settings, but the devices are still unable to boot.

anne_droid · Answer

Hi

The internet has a very long answer, and it is below, the short version try with SECURE BOOT=OFF.

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Microsoft is currently in the middle of a major “root‑of‑trust” refresh for its Windows Secure Boot certificates, not a general OS‑wide certificate change.

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For your environment (multiple Vostro 3515s purchased in 2021 showing the same symptom after 11‑May‑2026 Windows Update):

Temporarily disable Secure Boot on all affected units to get them booting.
Use a Windows recovery USB to run bootrec /rebuildbcd on any that fail to boot even with Secure Boot off.
Update BIOS to Dell’s latest revision for Vostro 3515 on all machines.
Re‑enable Secure Boot with factory keys restored, making sure OS Type = Windows UEFI.
Consider blocking or delaying the specific Windows Update that triggered this across your fleet until a Microsoft‑ or Dell‑certified fix is published.

Goal: Let the laptop boot so you can then repair or update properly.

Power off the machine completely.
Power it on and repeatedly press F2 to enter BIOS/UEFI Setup.
Go to the Secure Boot section (usually under Security or Authentication).
Set Secure Boot to Disabled (temporarily).
Save and exit (F10 → Yes).

If the laptop boots into Windows, proceed to step 3.
If it still fails, try step 2 (reset BIOS + Secure‑Boot keys).

This is important if the Secure‑Boot keys were mangled by a BIOS update or Windows‑induced policy change.

Enter BIOS/UEFI again with F2.
Go to Security → Secure Boot.
If present, set Secure Boot Mode to Custom.
Look for Reset all Keys / Clear Secure Boot Keys / Restore Factory Keys and run it.
Save and exit (F10).

Then power cycle, enter BIOS again, and:

Set Secure Boot Mode → Setup Mode.
Install/restore default Dell Secure‑Boot keys if prompted.
Then change mode back to Standard/User and set OS Type to Windows UEFI (not “Other OS”).

Re‑enable Secure Boot only once the machine boots cleanly.

If the laptop still will not boot even with Secure Boot disabled:

Create a Windows 11/10 USB recovery drive on another PC using Microsoft’s Media Creation Tool.
Boot the Vostro 3515 from USB (press F12 at Dell logo to enter one‑time boot menu).
Choose Troubleshoot → Advanced options → Command Prompt.
In the elevated Command Prompt, run:

text

bootrec /fixmbr bootrec /fixboot bootrec /scanos bootrec /rebuildbcd

These commands rebuild the Windows Boot Manager configuration.

If the BCD rebuild fails, you may need to run a Startup Repair from the same menu or consider an in‑place repair install (keeping data/apps).

Go to the Dell support site, enter the Service Tag of a Vostro 3515, and check the latest BIOS version.
If several units are affected after 11 May 2026, look for a BIOS update released around early 2026 that Dell explicitly notes as fixing Secure‑Boot or boot‑failure issues.
Apply the BIOS update offline from within Windows (do not interrupt power) and then re‑apply the Secure‑Boot key reset steps above.

Keeping BIOS on the recommended version can prevent this error recurring after future Windows Updates.

Vostro

DELL VOSTRO 3515 - AFTER WINDOWS UPDATE UNABLE BOOT

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