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Hi Marco Dell'Osa,
Here are some steps you can consider to follow:
- Safety first — backups and restore point
- Create a full system image or at minimum a system restore point and a user data backup to an external drive.
- Ensure a current recovery USB is available (Settings > Recovery > Create a recovery drive).
- Recommended free disk space: keep at least 30 GB free on C:.
- Pre-upgrade checklist (must complete)
- Update Dell firmware and drivers: BIOS, Intel chipset, Intel Management Engine, and NVIDIA drivers from Dell Support for G15 5530. Reboot after each firmware/driver install.
- Temporarily uninstall third-party AV/security agents and disconnect non-essential peripherals (external drives, docks).
- Disable disk encryption suspend (BitLocker: suspend until upgrade completes).
- Confirm Windows is activated and current build is healthy:
- Run as admin:
slmgr /xpr
DISM /Online /Cleanup-Image /RestoreHealth sfc /scannow chkdsk C: /scan
- Reboot after repairs.
3. Obtain the official 25H2 ISO
- Download the official Windows 11 25H2 ISO from Microsoft’s Download Windows 11 page. Use the Media Creation Tool to create an ISO or a bootable USB. Save the ISO to local storage.
4. Perform the in-place upgrade (interactive, keeps apps and files)
- Mount the ISO by right-click > Mount or run (PowerShell):
```powershell
Mount-DiskImage -ImagePath "C:\Path\to\Win11_25H2.iso"
- Note the mounted drive letter (for example, D:). From an elevated prompt run:
D:\setup.exe
- In the installer choose: Keep personal files and apps. Follow prompts and allow the upgrade to proceed interactively. Reboot when prompted.
Important notes:
- Do not choose Clean Install unless you want to wipe apps and settings.
- If the installer offers to download updates, allow it to do so—this helps avoid missing prerequisites.
- If the interactive installer fails or you want a more controlled upgrade
- Run setup with logging enabled and the compatibility hold bypass (useful when Windows Update blocks due to health checks):
D:\setup.exe /auto upgrade /compat IgnoreWarning /dynamicupdate disable /showoobe none /quiet
- I recommend running interactively first; use the above only if guided by logs and you understand it bypasses some checks.
- Collect logs if the in-place upgrade fails (essential for escalation)
- After a failure, gather these files and attach them for support or for further analysis:
- C:\Windows\Panther\Setupact.log
- C:\Windows\Panther\Setuperr.log
- C:$WINDOWS.~BT\Sources\Panther\setupact.log and setuperr.log (if present)
- C:\Windows\Logs\CBS\CBS.log (compress as CBS.zip)
- WindowsUpdate logs:
Get-WindowsUpdateLog -LogPath C:\Temp\WindowsUpdate.log- Device Manager export (devcon or pnputil list) and msinfo32 system summary (File > Save). - If you encounter 0x800f0991 again, include the exact timestamp of the failure and the contents of Setuperr.log lines around that timestamp.
- C:\Windows\Logs\CBS\CBS.log (compress as CBS.zip)
- C:$WINDOWS.~BT\Sources\Panther\setupact.log and setuperr.log (if present)
- C:\Windows\Panther\Setuperr.log
- C:\Windows\Panther\Setupact.log
- Specific mitigations for persistent 0x800f0991
- Ensure Servicing Stack Updates (SSU) and the latest Cumulative Updates are applied before in-place upgrade: manually download and install the latest SSU for your build from Microsoft Update Catalog then reboot.
- Boot into Safe Mode with Networking and uninstall any non-Microsoft drivers that may block servicing (virtualization drivers, older storage filters). Reboot and attempt the in-place upgrade.
- If an OEM driver is suspected, fallback to the generic Microsoft driver for storage or GPU temporarily (Device Manager > Update driver > Browse my computer > Let me pick > Microsoft Basic Display Adapter or Standard SATA AHCI controller), then retry upgrade. Reinstall Dell drivers after success.
- If disk errors were found, run offline CHKDSK: schedule chkdsk C: /f and reboot to complete.
- Post-upgrade validation
- Confirm installed version:
winver
or
systeminfo | findstr /B /C:"OS Name" /C:"OS Version"
- Validate activation:
slmgr /xpr
- Re-run:
DISM /Online /Cleanup-Image /RestoreHealth
sfc /scannow
- Re-enable BitLocker and reinstall AV and disconnected peripherals.
- If upgrade still fails — escalation checklist to provide to Dell/Microsoft
Provide the following in one ZIP:
- Setup logs listed in section 6.
- CBS.log compressed.
- HAR of the installer session if you used web-based updates.
- Exact error code, build numbers (current: 26100.6584), and timestamp of failure.
- Steps already taken (SSU, DISM/SFC, BIOS/drivers updated, in-place attempt using ISO). Ask support to check for specific driver or component that causes servicing stack rollback at the final phase (commonly storage, filter drivers, or driver verifier conflicts).
If you find this useful, please accept answer so that others can benefit too. Thank you :)
Regards,
Vivian