Step 1: Download Windows 7 USB/DVD download tool and install it.
This tool is available for free from Microsoft Corporation as well so you can get it from there too. Despite its name, this tool works with Windows 8 ISOs as well. You can use this tool for any version of Windows.
Step 2: After downloading and installing the tool, Run it , now you need to Browse and give the path where the ISO file is located in your computer.
Step 3: Now select whether you want to create a bootable DVD for windows or you want it to be a bootable pendrive. Here you need to select USB device because you want to make bootable pendrive.
Step 4: Browse and select the pendrive which you want to make bootable. Make sure that the pendrive has atleast 4 gb free . Now click on Begin Copying.
Step 5: Once you begin copying , the tool will start creating bootable Windows 8 USB installer flash drive using the Windows 8 ISO. Let this process complete , lastly when you see the message “Bootable USB Device created successfully”, you can restart your PC and boot from the USB drive.
So this was my Quick tutorial on how to Create Windows 7&8 Bootable USB, Hope this will help you.