How to make a USB Bootable on windows 7 or windows 8

Open the Command Prompt. You will need to run Command Prompt as an Administrator. Right-click on it and select Run as Administrator. You may need to enter the Administrator password.
Open the disk management utility. This can be opened by entering the command

diskpart

Display the connected disks. Type the command

list disk 

to show a list of all the drives connected to your computer. Your USB drive should be listed here as well. Make note of the number next to your USB drive.
Select the USB drive. Enter the command

select disk #

replace “#” with the number from the previous step.
Clean the flash drive. Enter the command

clean 

to have the disk management utility verify the integrity of the USB drive, and erase all data.
Create a bootable partition. Once the USB drive is clean, type in

create partition primary

You will see a message saying that the operation was successful.
Select the new partition. Enter the command

select partition 1 

and press Enter. Once you receive a confirmation message, type

active 

and press Enter. This will activate the partition.
Format the USB drive. Input the command

format fs=fat32 QUICK

Assign the USB a drive letter. Enter the command

assign 

to give the thumb drive a letter designation. Type

exit 

to end the disk management program
Copy the operating system. Once the USB drive has been made bootable, you can copy over the installation files for the operating system you want to install. You can do this by dragging and dropping using your preferred file manager/explorer
Use the bootsect to make the USB Drive bootable. This updates the drive with BOOTMGR compatible code and prepares it to boot Windows 7/Vista.

BOOTSECT.EXE/NT60 G: