1. Insert your usb disk into your computer.
2. Press Windows + R keys together.
3. Type cmd in the run box.
4. Type diskpart in the command prompt.
5. Click OK when the User Access Control Box is appeared.
6. Typelist disk in the command prompt.
7. You will see the disks.
8. Type select disk 1 or 2 or something (choose the usb disk number you want to make bootable).
9. Type clean in the command prompt.
10. Type create partition primary.
11. Type select partition 1.
12. Type active.
13. Type format fs = ntfs . (Wait until the format completes)
14. Type assign .
15. Copy the files from Windows Dvd or ISO or somewhere to the usb disk.
16. Now you can use this usb as a bootable disk .