I don't see anything on that link that says, "Download Now". Maybe that's an option during checkout (not in the UK, so I can't go there). All I'm saying is that I've never heard of being able to download Microsoft Windows from Amazon (purchased and delivered, sure, but not downloaded).
Also, when you do purchase Microsoft Windows 7, it comes on a DVD, not a CD. Windows 7 does not fit onto a CD. So if you are downloading the ISO and trying to burn it to a CD, the burn is probably failing and that would cause the OS install to fail as well.