Make existing Windows 10 installation bootable from USB

Solution 1:

Ah, INACCESSIBLE BOOT DEVICE seems to be a windows 10 favourite...

The first possible solution is outlined below, with an extra twist in case you need it. It seems to work for most people, but as your circumstances are slightly different we will have to see:

1. At the blue screen where the error appears, click Advanced Options
2. Click Troubleshoot
3. Look for an "Advanced Startup" or "Startup Options" menu
4. A list of boot options is displayed
5. Click Restart
6. Upon restarting you'll be taken to the boot options you previously saw in #4
7. Boot into Safe Mode by pressing the appropriate key
8. Once you're back into your desktop in Safe Mode, reboot your PC and everything should be back to normal.

If this doesn't work, during the restart that you trigger in step 5 enter the BIOS and change your SATA mode controller to IDE from ACHI, or vice versa, and try safe mode again. If that doesn't work it's time to look at setting up a USB recovery drive to tackle the problem.

The issue often seems to arrive from a changed SATA controller mode, which usually is done when changing from an HDD to an SSD, but as I said thing might be a little different here, hope it helps.

Additions based on comments:

I am aware that booting windows from a USB device is not natively supported, however I have myself achieved this in the past using a program which overcomes this limitation: WintoUSB. I have only ever used this to create "new" installs of Windows, but it may be possible to leverage the same ability to boot an existing Windows installation.

Solution 2:

Windows does not support boot from a USB disk.

Instead of booting directly from the external disk, you could use VirtualBox to build a virtual machine that boots from the external USB disk.

Here is one reference among the many that can be found :
Using a Physical Hard Drive with a VirtualBox VM.

Solution 3:

I fell over this article when I needed a copy of one of my physical machines. It had a hardware failure and I raided the disk, but before that I imaged it. When the replacement machine had a problem and I had to RMA it I wound up with a problem and decided to try and resurrect the original machine. Unfortunately with the repurposing of the existing C drive, I only had a disk image left and only a NVMe drive to put it on and only a USB adapter to put that in.

After a bit of searching I found the WinToUSB app and used the Windows To Go conversion on my existing disk from my laptop. Once done I tried to boot it.

Which wound with with Inaccessible Boot device. Now this is something I'm well used to with my Virtual Machine conversions, it is simply a matter of the USB driver not being set to start at boot (start type of 0), in the registry.

I also knew something else from my prior experiences with Windows To Go. If you install to USB2.0, USB3.0 will not boot.

I took the drive out of the USB3.0 slot and put it into USB2.0. I then booted into windows and logged in, opened up Regedit and navigated to Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services

I then took everything which looked like USB3.0 required to boot and set the Start value for each entry to 0.

I shut down the PC, swapped the drive from USB2.0 to USB3.0 and it booted fine. One Windows To Go from the existing install.

If you only have USB3.0 ports on the machine (some of mine do), you can plug the drive into another computer and use the article linked here, then take it out again and reboot it.

If you want to get all fancy and have VMWare workstation, you can connect it as a physical drive and boot into Windows to do the same.

Best, if you want to take an existing OS, is to change the start value before imaging the machine to USB.

Hope this helps and is not too late.