Help!!! I cannot get either of my ipods to display the icon once I plug the USB into the computer. Unable to sync.

Help, I cannot get either of my ipod touch's to display the ipod icon when I go to sync them with my library. So I cannot update them at all. I have a new DELL computer and an iPod touch 4th and 6th gen. I've tried a hard restart on the 4th and I've also restarted computer and tried different USB ports and cords. Nothing is helping.

While I'm at it, why can't I download standard def videos to my iPod classic anymore?