How to Install Windows Without a USB Drive (and Can You Use Your Phone?)

If your PC already runs Windows, you can reinstall or upgrade it without a USB drive. Download the Windows ISO from Microsoft, double-click it to mount it, and run setup.exe. Choose Nothing on the “Choose what to keep” screen for a clean install. You can also use Settings > System > Recovery > Reset this PC > Cloud download to reinstall the version you have. A PC with no working Windows at all still needs bootable media, like a USB drive, a DVD, or an external drive. A phone generally can’t stand in for one unless it’s rooted.

A quick note before you start: Windows 10 reached end of support on October 14, 2025. It no longer gets security updates unless you’re enrolled in Extended Security Updates, so if your PC meets the requirements, install Windows 11 instead. The steps below work for both.

Which method should you use?

Your situation	Best method
Windows starts, and you want a fresh start on the same version	Method 1: Reset this PC with Cloud download
Windows starts, and you want a clean install or a different version	Method 2: Mount the ISO and run setup
Upgrading from Windows 10 to Windows 11	Method 3: Installation Assistant
Windows won’t start, or the drive is empty	You’ll need bootable media. See the options below.

Method 1: Reinstall Windows with Reset this PC (Cloud download)

1. Back up anything you want to keep.
2. Open Settings > System > Recovery. On Windows 10, go to Settings > Update & Security > Recovery.
3. Next to Reset this PC, click Reset PC (or Get started).
4. Choose Keep my files or Remove everything.
5. Choose Cloud download. Windows downloads a fresh copy from Microsoft, about 4 GB or more.
6. Review your choices and click Reset. The PC restarts several times.

If Windows won’t start normally but you can reach the blue recovery screen, choose Troubleshoot > Reset this PC for the same options.

Method 2: Mount the Windows ISO and run setup

1. Go to Microsoft’s Download Windows 11 page and, under Download Windows 11 Disk Image (ISO), choose your edition and language, then click Download. For Windows 10, download the Media Creation Tool from the Windows 10 page, run it, and choose Create installation media > ISO file.
2. Open the Downloads folder, right-click the ISO file, and choose Mount. It opens like a DVD drive.
3. Double-click setup.exe and click Yes if User Account Control asks.
4. Follow the prompts. When you reach Choose what to keep, pick Nothing for a clean install, or keep your files and apps if you’re just repairing Windows.
5. Click Next, then Install.

You’ll need at least 20 GB of free space for the setup files, plus more for the installation. If Setup says your product key is needed, click I don’t have a product key. Windows activates automatically if the PC had a digital license. For more, see how to activate Windows.

Method 3: Upgrade to Windows 11 with the Installation Assistant

1. On Microsoft’s Download Windows 11 page, click Download Now under Windows 11 Installation Assistant.
2. Run the file and click Accept and install.
3. Leave the PC on while it downloads and installs. It restarts when it’s done, and your files and apps are kept.

The PC must meet Windows 11’s requirements, including TPM 2.0 and a supported processor. Run the PC Health Check app first to find out.

If Windows won’t start: options without a USB flash drive

A computer with no working Windows has nothing to run Setup from, so it needs to start from something else.

• Windows Recovery Environment. If the PC shows a blue Choose an option screen after a few failed starts, use Troubleshoot > Reset this PC > Cloud download.
• The manufacturer’s recovery partition. Many Dell, HP, Lenovo, and other PCs have a built-in recovery tool you open with a key at startup, like F11, F12, or F9. Check the maker’s support site for your model.
• A DVD. If the PC has a disc drive, burn the ISO to a DVD on another computer.
• An external hard drive or SSD. These work like a large USB flash drive.
• Another PC. You can remove the drive, connect it to a working computer, and set it up there, but this is best left to experienced users.

Can you install Windows from your phone?

Usually not. To install Windows, a PC must start from a bootable drive, and a phone connected by USB shows up only as a media device, not a drive the PC can start from.

• Rooted Android phones can use apps like DriveDroid to act as a bootable drive, but rooting can void your warranty, and results with Windows ISOs are hit or miss.
• Apps that work without root, such as EtchDroid, can write disk images to a USB flash drive plugged into your phone. The developer says official Windows ISOs from Microsoft aren’t supported, though, so this won’t help for Windows.
• iPhones can’t do either.

Your phone is still useful: you can use it to look up your PC’s recovery key or instructions while you work. If you need a bootable drive, a 16 GB or larger USB flash drive is inexpensive, and Microsoft’s Media Creation Tool can set it up on any working Windows PC. See how to install Windows on a PC.

Frequently asked questions

Will I lose my files?

Only if you choose Remove everything or Nothing. Back up to OneDrive or an external drive first either way.

Do I need a product key to reinstall Windows?

Not if Windows was already activated on the PC. It reactivates automatically with its digital license after you sign in and connect to the internet.

Is Cloud download better than Local reinstall?

Cloud download gets a fresh copy from Microsoft, so it works even if your local files are damaged. Local reinstall is faster and doesn’t use as much internet data.

Can I still download Windows 10?

Microsoft’s Windows 10 download page was still available after end of support, but Windows 10 no longer gets regular security updates. Use Windows 11 if your PC can run it.