There are a few reasons you'd want to boot your computer from a USB device. You might be trying to install Windows 10 or you might want to use a disk partition or clone utility that doesn't run within Windows.
There are several things that need to happen for your PC to boot from a USB drive. First you need a USB stick that has been set up to be bootable. Plus, your laptop or PC must be configured to look for USB devices before booting from its main hard drive. Here's how to make all that happen.
How do I make a USB stick bootable?
It sounds obvious, but your computer won't be able to start unless the drive is formatted correctly and has the appropriate files and software on it which enable it to boot.
A common mistake is to copy an ISO file to a USB drive and assume this is all that's needed for it to boot and install Windows, Ubuntu or another operating system. In fact, you need to use software which can write the files to the drive and also make it bootable.
With Rufus, you need to be a little careful about the settings you use, but for the most part, you just click the CD drive icon, choose an ISO file and make sure that 'Create a bootable disk using' box is checked.
These tools will warn you that they'll delete everything off your USB drive, so make sure you've copied off any files you don't want to lose before starting. You'll also need to have downloaded whatever software it is you're planning to boot from, be it Windows, Linux or something else.
How can I make my computer boot from USB?
Many PCs and laptops are set to check for a USB drive first before trying to boot from a CD, DVD or the internal hard drive. But not all are configured this way. You might find that plugging in your flash drive before pressing your computer's power button doesn't work: it just boots into Windows as normal, or does nothing if you've no operating system installed yet.
In this case, you need to look out for a message on the POST screen - the first thing you see on your monitor after pressing the computer's power button. The message is usually at the bottom of the screen and says something like 'Press F11 for boot options'.
Some PCs and laptops don't show this, so you'll have to check your manufacturer's website to find out which key to press, or even your motherboard manual.
Common keys to press when the POST screen is displayed are Delete, F2, F10 and F11.
The aim of this is to enter the BIOS as the computer starts up. Once in the BIOS, look for a menu or an option that lets you see and change the boot devices or boot priority. This will vary from BIOS to BIOS, but it's usually fairly obvious.
Make sure you change the first (#1) boot option, as whatever is set there will be the device that is tried first.
A tiny minority of old PCs may lack the ability to boot from USB, but anything within the last decade should have the option. If you're still having problems, check that USB ports haven't been disabled in the BIOS. Different BIOSes work in different ways, but use the information on screen to work out how to make a USB drive the first boot device.
Bear in mind that the USB stick may need to be plugged into a USB port for it to appear in the list of boot options.
Once you've set everything correctly, use the 'Save & Exit' option in the BIOS to save your changes and reboot the system (often this is the F10 key). Then your PC or laptop should boot from the USB drive when it restarts.
You might like to read our guide which explains how to build your own PC.