Q: my 2nd generation shuffle not appearing in itunes.  What can I do?

If you have not done so already, first try using a different USB port that is directly on the computer (not a hub). 

If that does not help, I would shut down (completely power off) your computer.  Disconnect the shuffle and do this reset procedure

http://support.apple.com/kb/HT1655

Start up your computer.  Run iTunes.  Try connecting the shuffle again.