I bought a new hard drive and I installed a clean copy of Windows 10 on it. Now I have the old hard drive which has my old copy of Windows 10 on it but I want to completely re-format the old hard drive and erase everything on it. Right now the old hard drive is not connected to my motherboard because I am afraid of connecting it because then I will have two different copies of Windows 10 hooked up to the same motherboard. So what should I do? Can I hook up the old hard drive and format it through Windows or do I need third party software or what? I know how to hook up the old hard drive and boot up to the new one from the BIOS screen, but I am lost after that. I don't want to damage anything. Any help would be appreciated.