Need to boot your PC from a USB stick, or optical drive, to install or try out a new operating system? Maybe you've run into a common problem: even though you've inserted the USB drive or CD/DVD, the computer won't boot from it!

To fix this, you'll need to change the boot order for your system, setting the preferred device as the primary boot drive. Sounds complicated, but it isn't. Here's what to do.

Why You Might Want to Change Boot Order

There are various reasons why you might want to change the boot order.

For instance, you might have added a new hard disk drive and want to use it as your primary boot device; changing the boot order will enable you to install your operating system.

Alternatively, you might have problems booting Windows. Setting an optical drive or USB drive as the primary device will allow you to use a disc, flash storage, or external HDD to provide assistance to recovering data or repairing the operating system.

Solutions for these problems include installing Windows from a USB drive, or using a multiboot USB device to install a new operating system.

Understanding Your PC's Startup Procedure

What happens when you start up your PC? In most cases (and putting it very simply), after the power switch has controlled the flow of electricity to the motherboard and the fans have started up, your hard disk drive will be initialized and start reading the boot sector.

From here, the operating system will load in from the hard disk drive to RAM. If there is no operating system, or the OS has been compromised, then it'll need to be repaired or replaced. Neither option is possible, however, without a bootable operating system installer.

To use an alternative boot device, you need to tell the computer that you have changed the boot drive. Otherwise it will assume you want the usual operating system on startup. To change the boot device, you'll have to access the boot menu in the BIOS.

How to Access the BIOS Screen

There are different ways for you to access the BIOS screen. You need to be quick with your fingers, be close to the keyboard when you switch the computer on, and make sure that your monitor/display is already switched on, otherwise you might miss the instruction!

What happens is that a short line of text---usually across the bottom of the screen---will indicate which key you need to press to launch the BIOS screen. This is often the Delete key, but might also be F1, F2, or one of the other function keys.

In some cases you may need to reset the computer if it progresses through to loading Windows too quickly. We would advise waiting for Windows to load (assuming you're not experiencing any Windows loading problems) rather than pressing the reset button, as this can cause problems later on.

Note that if you have a password set on your BIOS, this will be required before you can access any of the menus and options.

How to Access the BIOS Boot Order Menu

Once you have logged into the BIOS, you will need to find the Boot menu. You'll find this labelled Boot on older BIOS screens, but it can also be found as a sub-menu under System Configuration, and is accessed by navigating with the left/right arrow keys (these and other controls are usually displayed as a legend at the bottom of the screen).

It doesn't matter whether your system uses traditional BIOS or UEFI (here's how to check), the Boot menu can be accessed in generally the same way.

A BIOS boot screen

In the Boot order menu, you will need to use the Up and Down arrow keys to select an item and probably tap Enter to select it. This might open up a secondary menu which you will again use the arrows to navigate and Enter to confirm your choice.

Note: In some BIOS menus, there may be no option to select. Instead the Page Up/Page Down keys will be used to cycle the boot item up and down through the list. Once again, check the legend at the bottom of the screen.

Once you have changed the boot drive, you will need to save the change. You should see a menu option labelled Save and Exit, so navigate to this and use the arrow keys and Enter to save the changes. Many motherboards offer a keyboard shortcut for this command, often F10.

With this step completed, the computer should restart, allowing you to access the chosen boot device.

Related: How to Boot From USB on Windows

Alternatively, Use the Dedicated Boot Menu

Increasingly, computers are being shipped with an additional menu that lets you change the boot order without accessing the BIOS.

How to do this will differ depending on your PC or laptop's manufacturer. However, the correct command (typically Esc or F8) will be displayed when your computer boots, along with the BIOS message. Once this screen has opened, all you need to do is highlight the device you wish to boot from using the arrow keys, then Enter to select.

Select a USB device to boot your PC
Image credit: Wikimedia Commons

Once you've made your choice, use the arrow keys to select your USB drive, apply the change, and reboot. Your computer will then restart, and boot from the USB device.

Note: On Windows computers, once the BIOS POST screen has closed, the F8 function is disabled and used by a different function: the Windows Advanced Boot Menu.

How to Boot From USB in Windows 10

Keeping everything above in mind, if you want to boot from USB in Windows 10, the process is simple.

Begin by connecting the bootable USB drive, then in Windows 10 open Settings (Windows key + I), then Recovery. Find Advanced startup and select Restart now. In the next screen, select Use a device, and when you see your USB drive listed, tap or click this.

Your computer will then restart, and boot into the environment (or installation wizard) on the USB disk.

Easily Change the Boot Order in Windows 10

Now you should be able to change the boot order of your PC without issue. While it might seem an unfamiliar environment, it's a simple five-step procedure:

  1. Insert the bootable USB drive.
  2. Restart the computer.
  3. Tap the key to open the BIOS or boot order screen.
  4. Select the USB device or whatever other boot drive.
  5. Save and exit.

You'll then be free to repair your computer, or reinstall Windows from the USB drive.