I bought a used laptop that originally had Windows 7 on it, and the previous owner upgraded to Windows 10. I'm having problems with some hardware that I bought this laptop for which apparently isn't yet supported for Windows 10 so I need to go back to 7. I have the key on the sticker on the bottom but no disk. Can I download it somewhere? Also the laptop had no disk drive only USB ports. So I'm guessing I'll need to put the OS on a USB drive? Thanks.