create a bootable usb disk

1) Run diskpart from command prompt running as administrator (right click the command prompt icon and choose "Run As Administrator")
2) Type the command: list disk to see the available disks and note the one that represents your USB thumb drive
3) Select the disk: select disk # where # is the disk you determined in the above step
4) Now that the proper disk is selected, prepare it with the clean command by typing clean
5) Now create a partition on the clean drive by typing: create partition primary
6) Select the new partition by typing: select partition 1
7) Set the partition as active by typing: active
8) Format the partition as FAT32 by typing: format fs=fat32
9) Assign the new partition by typing: assign
10) Type exit to quit diskpart

And some files which are needed for boot the computer can be copied to the disk.