I got new laptop with 8.1 on it and I wanna kill 8.1 to the last bit and install windows 7 on it. I tried with Killdisk disk and USB and Lenovo UEFI/BIOS doesn't allowed it. I don't want just to format it with windows 7 installation disk so there are traces after it. Is there a way to kill it for good? Any software or method?