Try a reset. To reset an iPod Classic, turn the lock button on, then off and then press-and-hold both the Menu and the Select (centre) buttons together for at least ten seconds. During this time, the Apple logo should appear. If it does, the iPod should re-start.
If that doesn't sort it out, try that method again (up to three times). If that still doesn't fix it, follow the Five R's procedure, which begins here; http://www.apple.com/support/ipod/five_rs/classic/
Finally, there is one more thing. If the iPod is "stuck" trying to do something, the best thing to do is leave the battery to run down. The usual symptom in this case is that the display is on, but nothing responds. Letting the battery run down will cause the iPod to reset when re-charged. Hopefully, you won't need to go to this extreme.