Hi Try this to fix the problem: (its from the Itunes help menu)
To add songs to iPod manually:
Connect your iPod to your computer.
When the iPod icon appears in the iTunes window
(under Devices), select it.
If the Summary pane is not showing, click the
Select "Manually manage music." (If you have an
iPod that displays video, the checkbox says "Manually manage music and
Click Music (below Library, on the left side of
the iTunes window) and then drag songs and playlists to your iPod.