My ipod is not showing up on my itunes screen anymore and therefore will not sync anymore of the new songs i have purchased. How can i correct this?

For years when i would plug my ipod into my computer, it would show up in the left top corner of my itunes screen and then i could sync the new songs i purchased onto it. Now the ipod icon no longer shows up. a screen appears saying ipod support is not downloaded. When asked if I want to load it, I push yes. Then an error box comes up and says it can't download it. SO, at this point I can no longer load my new purchases on my ipod. ****** about that!!