Insert flash drive (flash disk) in the USB port of your computer
Open command prompt (cmd) as administrator
Enter the following commands on command promp:
diskpart
list disk
select disk z
z is the number corresponding for your USB disk. Replace it with the corresponding letter from your own system. BEWARE and CHECK that you choose your flash drive disk
clean
create partition primary
active
format fs=fat32 quick
assign
exit
Open windows explorer
Copy the whole file of windows (from windows CD) to flash drive (flash disk)
Restart PC, dont forget to enable boot from USB
*credit to bootableusb.net