How Can I Create the USB Drive From a Windows 8.1 DVD or ISO file?

If you already have the Windows 8.1 DVD or ISO file, you will first have to copy the contents of the DVD or ISO into a folder on the internal storage of the device. You can use 7-Zip orWinRAR to extract the contents, if the file cannot be mounted. Please make sure the location you choose has more free space available than the size of the media -- more than 4 GB should suffice.

After you have copied or extracted the contents, follow the next steps:

1. Open the Command Prompt. This can be done by triggering the Run -- Windows Key + R -- feature, and opening "cmd".
2. Type "diskpart" to open the disk partitioning software. Accept the UAC security prompt, if asked.
3. Insert the USB drive.        
4. Type "list disk". The program will then show you a list of all the physical drives (HDD, SSD, USB, etc.) that are attached.
5. Identify the disk number of the USB drive (it can be recognized by looking at the size column; it's usually the last listed disk) and type "select disk X", where "X" is the disk number of your USB drive.
6. Type "clean". This will erase the contents of the USB drive, so make sure you have the contents backed-up beforehand.
7. Type "create partition primary". This command will create a primary partition on the USB  drive.
8.  Type "select partition 1". This command will select the created partition.
9. Type "active". This command will make the selected partition active.
10. Type "format fs=ntfs quick". This command will format the created partition as NTFS.
11. Type "assign". This command will assign a letter to the USB drive, which will make it show under Windows Explorer.
12. Copy the contents of the Windows 8.1 DVD or ISO from the created folder on the USB drive.