Why create (UEFI) bootable USB?
(UEFI) Bootable USB, just as its name implies, is used to boot non-OS computer or OS corrupted machine.
Bootable USB drive can help to repair system when your OS fails to boot.
Bootable USB stick can assist you back up the hard drive without booting Windows when Windows is unbootable due to damaged boot files.
It can help you to install operating system. For example, if you want to install Windows on other hard drives or other computers and you don’t have an installer disc around, it is time to create (UEFI)bootable USB key using Diskpart or other tools. This bootable drive has all the necessary Drivers to boot the machine. So downloading an ISO file to the bootable drive makes the preparation done.
However, either to use third party software or to use Diskpart in Windows, you have to figure out how to create a bootable USB.
Diskpart to create bootable USB
Tips: This part will introduce you how to create (UEFI) bootable USB using
Diskpart. Note that all operations in Diskpart are irreversible. If you are not
familiar with Diskpart commands and want to take less risk of losing data, skip to
next part directly.
Firstly, insert an USB drive into running computer. All data in the
USB drive will be formatted, you can backup files before reformatting. Open a Command Prompt window as an administrator, and
type diskpart. Remember press Enter key after your each
move.
Secondly, type the following commands in order.
1. list disk
2. select disk X (X stands for the drive letter or disk number of your
USB drive)
3. clean
4. create part pri
5. select partition 1 (this is the partition you just created)
6. assign letter=N
7. select partiion N
8. format fs=ntfs quick (if you want to create UEFI bootable USB in
Diskpart, format it as FAT32. Type format fs=fat32 quick instead)
9. active
10. exit
Finally, place your prepared custom image onto the root of the USB
flash drive. Pay attention to that if your USB showing as Removable
Disk in Windows Explore, you can only create one primary partition there. If it shows as Fixed Disk, you can create multiple primary
partitions in accordance with its size.
Create bootable USB for repairing via AOMEI Partition Assistant
Diskpart to create bootable USB in Windows 7, 8.1 is effective and advanced
operation. If you are a novice to computer and looking for more graphical and easier
solution to create bootable USB stick for repairing Windows, you can try AOMEI Partition Assistant Professional.
You can download its demo version to have a try!
This partition tool has a user-friendly interface and you can finish making bootable
USB in fewer steps. The most important thing is you don’t need to prepare custom
image (ISO.file) again because Partition Assistant takes care of that. It provides Create Windows PE Bootable Media to
follow. No need to worry about potential mistakes you may make. What’s more, burn
Partition Assistant into bootable device and boot from bootable device to manage
hard drive, you can manage a mass of computers without directly install the software on these machines.
Step1. Install and start AOMEI Partition Assistant. Click Make
Bootable Media in the left pane.

Step2. Click USB Boot Device to select your USB
drive as the path to store ISO file, and click Proceed.

Step3. Click Yes in the pop-up window, and
wait for the process completes.

When the process is done, connect the bootable USB drive into the computer with boot issue, change boot order to boot from the bootable USB stick. And then you can fix Windows OS through rebuilding MBR or check whether there are bad sectors on the partition.
All in all, it is easy to use Diskpart create bootable USB drive yet using AOMEI
Partition Assistant is much more convenient indeed. After booting from the bootable
USB drive created by AOMEI Partition Assistant, you can also use its other functions, like resize partition, copy disk, copy partition, create partition in Windows from C drive, etc. If you are running Windows 8, 8.1, or
10, you can make a Windows To Go USB drive via AOMEI Partition Assistant.