iPod not showing up
For the iPod not being recognised, see this article:
iPod missing in "My Computer or in iTunes on Windows:
http://docs.info.apple.com/article.html?artnum=61711
"Do not disconnect" message
The "Do Not Disconnect" message is perfectly normal if your iPod is manually managed, or is set to automatic sync but you have disk use enabled. It's possible some settings have been changed accidentally to give one of these.
To check which you have, connect the iPod, open iTunes, go to edit>preferences>iPod.
If you are manually managing songs you will always need to eject the iPod after each connection by clicking the small icon at the left hand source pane next to the iPod in iTunes.
If on the other hand you are automatically syncing music, uncheck disk use on the preferences page and your iPod will automatically disconnect after each update is complete.
For more information on disconnecting and the "Do Not Disconnect" message, see these:
About the "Do Not Disconnect" and "OK To Disconnect" screens on iPod:
http://docs.info.apple.com/article.html?artnum=61685
Safely Disconnecting the iPod:
http://docs.info.apple.com/article.html?artnum=61135
