First you need to download an ISO of Windows 7. If you plan to install Windows 7, then make sure you download the version you have the key for. If you plan to eventually install Windows 8, then you can select any file, but make sure you choose between 32 and 64 bit correctly.
STEP 2: DOWNLOAD WINDOWS 7 USB DVD DOWNLOAD TOOL
Download from here:
Contrary to its name, it isn’t a tool for downloading Windows, but it is a tool that copies the ISO file to a USB stick.
When the ISO has downloaded, run the program. In the first screen, click ‘browse’ and find the ISO file.
On the next screen, click USB.
Insert your USB stick (make sure there’s nothing valuable on it before you start!) and select it from the list. You might need to click the ‘refresh’ button if you don’t see it at first.
STEP 3: INSTALL WINDOWS 7
Plug the USB stick into the computer you wish to install Windows on, and turn it on. Hopefully, the computer will automatically start to load from the USB stick. If not, you might have to try and bring up the boot options in the BIOS when the computer starts up. Try mashing some combination of F2, F8, F10, F12 or DEL one at a time and see if you can bring up a menu with an option like ‘boot from USB. Or try googling your laptop/motherboard model number and ‘boot from usb’.
Follow the instructions on screen. If you are prompted for a key, only enter it if you intend to install Windows 7 in the end. This whole step should take about an hour.