which windows are you currently using?!
if itx win7 then follow dese stepx .. em sure these will help you out
1. first of all plug your Usb flash drive in
2. Start - on da search baar write 'RUN"
3. cmmand screen will appear - write on "Diskpart" .. it will open another black windows
4. type "list disk" .. it will let you see all available flash disk or hdd you had connected to your pc
5. select da disk number of your flash disk .. like "select disk 1"
6. now type "clean"
7. write "create partition primary"
8. "select partition 1"
9. "active"
10. "format fs=fat32"
11. after a complete and clean format type "Assign" and then "exit"
12. manualy copy all windows installation files to your flash disk !
your Done
P.s: All these sign "" are not included .. they are just fo da user to easly pick da cmmand
Thankyou!