I recently made several system images of my pcs with win 7. I saved them to an external drive and tried copying to another external drive. When I do, it shows either 0kb or 16kb and sits for a long time copying and wouldn't copy all the images. Also I had one image on 2 dvd discs, I tried to make an iso of it and stick it on the external drive but said the format wasn't valid or something. How do I properly make backups of these system images??