If you have iTunes 11 turn on the Sidebar. Go to iTunes>View and click on Show Sidebar. You can also do a Crtl+S to show the sidebar. The sidebar is where Devices appears. and Control+B to show the Menu bar
Did you do everything here:
New cable and different USB port?
Runs this and see if the results help with determine the cause
Try on another computer to help determine if computer or iPod problem