How to create bootable USB drive
1) there should be .iso file of windows (7 or 8)
2) install virtual dvd drive software e.g magic iso or power iso
3) mount the windows 7 .iso image to virtual dvd drive
4) open cmd as administrator
5) TYPE COMMAND
LIST DISK
SELECT DISK # /* where # is the your flash drive
CLEAN
CREATE PARTITION PRIMARY
SELECT PARTITION
ASSIGN
FORMAT FS=NTFS QUICK
ACTIVE
EXIT
XCOPY /S/E/F S:\*.* D:\ /* after /s/e/f S is your source drive (virtual drive)
D is your flash drive