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You can start Windows 10 Setup without a USB drive or DVD if the PC still boots into Windows: download Microsoft’s ISO, mount it in File Explorer, then run setup.exe from the virtual drive. If you choose Keep nothing, Setup removes personal files, settings, and apps. However, Microsoft’s documented booted clean-install process uses installation media; the mounted-ISO route should not be treated as the same partition-formatting workflow.
What “clean install” means when you run Setup from an ISO
Microsoft says you can install Windows 10 directly from an ISO without a DVD or flash drive by mounting the ISO file. This starts Setup from within the Windows installation that is already running; it is not the same as booting the PC into an installer. Microsoft’s Windows 10 download page documents the mounted-ISO route, while its reinstallation instructions describe booting installation media for a clean install.
During an in-place Setup run, you may be offered choices about what to keep. Microsoft says Keep nothing removes personal data, settings, and apps. That is destructive, but the cited instructions do not establish that running Setup from a mounted ISO formats the Windows partition or erases every disk. If you specifically need the booted installer’s partition-selection and formatting workflow, use bootable installation media instead.
Before you start
- Make sure Windows starts and you can sign in. Mounting the ISO and running Setup depends on the existing Windows environment. This method is not a fix for a PC that cannot boot into Windows.
- Back up files you need. Microsoft recommends backing up personal files before reinstalling. Use a location such as an external hard drive, USB flash drive, or cloud storage. A backup device is optional for this installation method, but keeping a separate copy of important files is prudent before choosing Keep nothing.
- Check activation and edition. Confirm Windows is activated and note which edition is installed. Microsoft says the edition being reinstalled must match the license. A device with an existing Windows 10 digital license can usually reinstall the same edition without entering a product key and activate online afterward. A major hardware change, such as replacing the motherboard, can require activation troubleshooting. See Microsoft’s Windows activation guidance.
- Consider support status. Windows 10 support ended on October 14, 2025. Microsoft says free Windows Update software updates, technical support, and security fixes ended then and recommends moving to Windows 11. Reinstalling Windows 10 does not restore those free updates. See Microsoft’s installation-media guidance.
How to start Windows 10 Setup from an ISO without USB or DVD
- Download the ISO from Microsoft. Open the Windows 10 download page and obtain the ISO. Avoid unofficial ISO mirrors.
- Mount the ISO. In File Explorer, find the downloaded ISO, right-click it, and select Mount. Windows displays its contents as a virtual DVD drive. If Mount is not shown, make sure the file is an ISO and use File Explorer’s context menu options.
- Run Setup. Open the new virtual drive and double-click
setup.exe. Follow the on-screen prompts to begin installation. - Review the keep option carefully. Setup may ask what to keep. Choose Keep nothing only if you intend to remove personal files, settings, and apps, and have already backed up anything important. Other choices depend on the options Setup presents for your current installation.
- Complete Setup. Continue through the prompts and allow the PC to restart as needed. After installation, connect to the internet and check activation in Windows Settings. If the same edition is installed on a device with a valid digital license, it will typically activate online.
Which Windows reinstall route should you use?
| Route | Does Windows need to boot? | USB/DVD required? | When it fits |
|---|---|---|---|
Mounted ISO and setup.exe |
Yes; Setup runs from Windows. | No. | Start Setup from a working Windows installation. Keep-nothing removes personal data, settings, and apps, but the official instructions do not establish it as the booted partition-formatting workflow. |
| Bootable installation media | No; the PC starts from the media. | Yes, bootable media is required. | Use this for Microsoft’s documented clean-install path, including when Windows cannot start. Installation can erase data on the selected installation. |
| Windows recovery options | Depends on the recovery option and whether Windows or its recovery environment is available. | Not necessarily. | Consider options such as Reset this PC or System Restore when their particular effects suit the problem. These options are not all equivalent to a clean install; review Microsoft’s recovery options. |
If Windows will not start
The mounted-ISO procedure cannot be relied on when Windows will not start, because it requires a running Windows session to mount the ISO and launch Setup. Microsoft’s documented clean-install instructions use bootable installation media. Review Microsoft’s installation-media guidance and recovery options to choose a route appropriate to the PC’s condition.
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- can be installed on HDDs, SATA SSDs, and NVMe SSDs; while HDDs work, they’re slow, SATA SSDs are much faster, and NVMe SSDs provide the best performance.
- Windows 10, installation works best with a drive using the GUID Partition Table (GPT) and UEFI boot mode, but it can also install on Master Boot Record (MBR) drives using Legacy BIOS.
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