You don't need to backup your whole PC. Backing up the windows folder is useless as that Windows is expired. Backing up program files is useless as you'll have to reinstall all your programs anyways once you reinstall Windows. Really you just need to backup downloaded stuff, pics, documents, etc, that you want to keep. Trying just copying the stuff to your external drive, keeping the copying small so it doesn't reboot after 2 hours. Copy just your pics, then see how much time has went by, if you still have an hour, try to copy a few more GB and go from there.