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Start in Windows Recovery Environment (WinRE), protect access to your files, then try Startup Repair. UNMOUNTABLE_BOOT_VOLUME is an error message, not a diagnosis: Microsoft’s general stop-code guidance does not establish what caused this particular failure or guarantee that one repair will work. Use the least disruptive suitable recovery option first, and avoid resetting or reinstalling Windows until you understand the possible effect on your data.
Before you try to repair Windows
If you can’t risk losing files that are not backed up, pause before choosing Reset this PC or reinstalling Windows. Microsoft warns that some recovery options can cause data loss, and reinstalling Windows from installation media removes everything from the device. When files are irreplaceable, consider getting qualified local diagnosis or data-recovery help before taking a more disruptive step.
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If BitLocker is enabled, locate your recovery key before starting. Microsoft says the key is needed for most WinRE recovery options. Microsoft’s recovery-options guide describes the available choices and their data implications.
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Enter Windows Recovery Environment
WinRE is Microsoft’s built-in starting point for Windows startup recovery. A PC may enter it automatically after repeated startup failures. If it does not, use one of the available routes below.
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- Windows still opens: Go to Settings > System > Recovery, then select Advanced startup and choose Restart now. You can also hold Shift while selecting Restart from the sign-in screen or Start menu.
- A manufacturer recovery button or menu is available: Use the instructions for your PC model to open recovery.
- You have Windows installation media: Boot the affected PC from the media. Choose your language and other preferences, select Next, then select Repair my PC to open recovery tools.
Microsoft documents these routes in its Windows Recovery Environment guide.
Run Startup Repair first
- In WinRE, select Troubleshoot > Advanced options > Startup Repair.
- Select Restart if prompted, then follow any on-screen instructions.
- If Windows still will not start, note any report or message and return to Troubleshoot > Advanced options to choose a next step.
Startup Repair automatically checks for common startup problems and attempts to fix them; it may report that it could not repair the issue. It is a sensible first attempt, not a guaranteed fix for UNMOUNTABLE_BOOT_VOLUME. See Microsoft’s Startup Repair instructions.
Choose the next recovery option based on what changed
In WinRE, use Troubleshoot > Advanced options to find the recovery tools. Start with the option that best matches when the boot failure began. If there was no recent change, don’t assume an update caused the error.
If the problem began after a Windows update
Choose Uninstall Updates and follow the prompts. This is relevant when the startup problem followed a recent update; it is not evidence that every occurrence of this error is update-related.
If you have a suitable restore point
Choose System Restore and select an available restore point. Microsoft’s current recovery guide also lists point-in-time restore for supported Windows 11 version 24H2-or-later setups; availability depends on the Windows version and configuration. Follow the prompts and review the effects described on screen before proceeding.
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If built-in recovery has not worked
Reset this PC and reinstalling Windows are more disruptive choices. Read each screen carefully so you understand what will be kept or removed. If you reinstall Windows from installation media, Microsoft warns that the process removes everything from the device. Back up files first wherever possible; if you cannot protect important data, seek qualified help rather than proceeding blindly.
Microsoft’s recovery-options guide explains the available paths and advises starting with the least disruptive appropriate option.
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Create installation media if you cannot reach WinRE
If you do not have recovery media, create Windows installation media on another working PC using a USB drive with at least 8 GB of capacity. Creating a recovery drive erases the USB drive’s contents, so use an empty drive or copy its files somewhere safe first. Follow Microsoft’s instructions for creating and using recovery media. The USB drive gives you a way to access recovery tools; it does not itself repair the error.
When to stop and get help
- Work- or school-managed PC: Contact your IT department before resetting or reinstalling Windows.
- Files are at risk: Stop before options that may erase data and seek qualified local support or data-recovery advice.
- Recovery tools fail or the problem persists: A qualified technician can assess whether the cause requires diagnosis beyond the available Windows recovery steps.
Microsoft’s general stop-code troubleshooting guidance covers Windows stop errors broadly; it does not identify the cause of this specific message on an individual PC. Avoid treating a particular cause or command-line fix as certain without a diagnosis.
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