If you are trying to make Pen-drive bootable, you can do this by using cmd prompt.

Follow the below steps- First make sure to insert the usb drive and then go to Command Prompt---> press start+r key to open run and type cmd in to open command prompt.

Then type these commands-

1. Diskpart and press enter-> this will show you users account control popup and you have to select yes.

2. DiskPart> listdisk : This will list out the disk on your drive, after this you have to select the disk.

3. Diskpart> select disk 1

4. Diskpart> clean ---> This will clean your disk.

5. Diskpart> create partition primary.

6. Diskpart> select partition 1

7. Diskpart> active

8. Diskpart> format fs=ntfs quick
   You have to wait until the format is done.
   
   When diskpart is successfully formatted then continue with the following commands.

9. Diskpart> assign

10. Diskpart> exit (this will exit the diskpart function)

11. After exiting go to my computer

12. Find the windows 7 or which u have an ISO image

13. Now you need tool to open iso image many software came like i.e magiciso, winrar, demon tools.

14. Now right click on your iso file and open it with any tool which u have i.e magiciso, winrar, demon tools etc.

15. Now select all the files and drag it to that partition which we have created.