1) Go to command prompt
2) Type diskpart
3) Put your pen drive on the PC with at least 4 GB capacity 8 GB will be better. Then type list disk
4) Select the disk which is your pendrive.
5) Now you have to run different commands
> clean > create partition primary > select partition 1 > active > formatfs=fat32
These steps are shown in the below image
6) After format is complete (Format may take long time):
> assign > exit
– The image below shows the detailed steps:
7) After the format is complete copy all the contents of windows 7 DVD and paste it in USB drive. Now your USB is device is ready to boot windows 7.